Energy & Fuels 1996, 10, 679-683
679
Performance of Different Catalysts on the Coprocessing of a Demineralized Catalan Lignite Christophe Bengoa, Josep Font, Angel Moros, Agustı´ Fortuny, Azael Fabregat,* and Francesc Giralt Departament d’Enginyeria Quı´mica, Escola Te` cnica Superior d’Enginyeria, Universitat Rovira i Virgili, Carretera de Salou, s/n, 43006 Tarragona, Catalunya, Spain Received July 18, 1995X
This work studies the influence of Fe, Fe-Mo, Co-Mo, and Ni-Mo catalysts on the coprocessing of a lignite from the Bergueda` (Catalonia, Spain) with a vacuum residue of petroleum. Given the high mineral matter content of this lignite, it was demineralized to prevent any interference with the catalyst performance. A set of supported Fe-based catalysts as well as two commercial hydroprocessing catalysts were tested. The experimental results show that coal conversion increases with all catalysts, although those containing molybdenum yield the largest values (5060%). The percentage of iron in the catalyst does not have a strong influence on this conversion, suggesting functional problems. Significantly high coal conversions are also obtained in experiments with alumina (≈40%) or without catalyst (≈44%), suggesting that the demineralization process causes fragmentation of the coal structure. The production of oils is larger with the Mo-based catalysts (19-25%) and on the order of 8% for the Fe-based catalysts.
Introduction The distribution of oil-derived products is increasingly turning toward light distillates such as motor fuels and petrochemical feedstocks at the expense of heavy fuels. In addition, the use of potentially contaminant fuel-oils is largely penalized because of environmental constraints. These trends refocus the refining strategies, and large stocks of heavy ends have to be converted into clean light products.1 The coprocessing of coal with a heavy end, i.e., a vacuum residue, is a low-cost route for upgrading, which also enables us to obtain additional oils from the coal. However, the petroleum residues are poor hydroaromatic solvents and hydrogenative atmospheres and catalysts are needed to improve the quality of the products. Thus, the study of suitable catalysts is a critical step for the success of coprocessing. Iron compounds are well known as being active catalysts in coal liquefaction reactions,2 and Fe-based catalysts are still the object of research at present.3-14 Most previous studies agree that iron in sulfide form selectively catalyzes the cleavage of C-C bonds.3-5 In Abstract published in Advance ACS Abstracts, March 15, 1996. (1) Be´lorgeot, C.; Boy de la Tour, X.; Chauvel, A. Refining and Petrochemicals. The New Deal. Profils IFP 94.2; Institut Franc¸ ais du Pe´trole: Paris, 1989. (2) Derbyshire, F. Role of Catalysis in Coal Liquefaction Research and Development. Energy Fuels 1989, 3, 273-277. (3) Farcasiu, M.; Smith, C.; Pradhan, V. R.; Wender, I. Iron Compounds and Iron Catalysts: Activity in Reactions Relevant to Direct Coal Liquefaction. Fuel Process. Technol. 1991, 29, 199-208. (4) Tang, Y.; Curtis, C. W. Activity and Selectivity of Slurry-Phase Iron-Based Catalysts for Model Systems. Energy Fuels 1994, 8, 6370. (5) Zmierczak, W.; Xiao, X.; Shabtai, J. Hydrogenolytic Activity of Soluble and Solid Fe-Based Catalysts as Related to Coal Liquefaction Efficiency. Energy Fuels 1994, 8, 113-116. (6) Das Gupta, R.; Mitra, J. R.; Dutta, B. K.; Sharma, U. N.; Sinha, A. K.; Mukherjee, D. K. Effect of Iron and Sulphur Dosage in Coal Liquefaction: Modelling and Optimisation. Fuel Process. Technol. 1991, 27, 35-43. (7) Dadyburjor, D. B.; Stewart, W. R.; Stiller, A. H.; Stinespring, C. D.; Wann, J. P.; Zondlo, J. W. Disproportionated Ferric Sulfide Catalysts for Coal Liquefaction. Energy Fuels 1994, 8, 19-24. X
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addition, it has been reported that increasing dosages of iron in the catalysts improves coal conversion and even reduces the production of asphaltenes.4,6,7 However, Fe-based catalysts show low activity in the hydrogenation of the coal products. Their performance could be increased using molybdenum as a doping metal.8 The influence of several Fe-based and commercially supported catalysts on the coprocessing of the Bergueda` lignite has been reported in previous studies,15,16 which found that coal conversion using these catalysts was comparable to that obtained in uncatalyzed tests. The poor performance of the catalysts was attributed to the interference of the mineral matter present in the lignite. Although the catalytic properties of the mineral matter present in the coal are well known, their removal is desirable because it prevents poisoning of the cata(8) Pradhan, V. R.; Herrik, D. E.; Tierney, J. W.; Wender, I. Finely Dispersed Iron, Iron-Molybdenum, and Sulfated Iron Oxides as Catalysts for Coprocessing Reactions. Energy Fuels 1991, 5, 712-720. (9) Bacaud, R.; Besson, M.; Djega-Mariadssou, G. Development of a New Iron Catalyst for the Direct Liquefaction of Coal. Energy Fuels 1994, 8, 3-9. (10) Mochida, I.; Sakanishi, K.; Sakata, R.; Honda, K.; Umezawa, T. Design of Recoverable Catalysts for a Multistage Coal Liquefaction Process. Energy Fuels 1994, 8, 25-50. (11) Zhao, J.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Binary Iron Oxide Catalysts for Direct Coal Liquefaction. Energy Fuels 1994, 8, 38-43. (12) Ibrahim, M. M.; Seerha, M. S. Testing Fe-Based Catalysts for Direct Coal Liquefaction Using in Situ Electron Spin Resonance Spectroscopy. Energy Fuels 1994, 8, 48-52. (13) Sanjay, H. G.; Tarrer, A. R.; Marks, C. Iron-Based Catalysts for Coal/Waste Oil Coprocessing. Energy Fuels 1994, 8, 99-104. (14) Stohl, F. V.; Diegert, K. V. Development of Standard Direct Coal Liquefaction Activity Tests for Fine-Particle Size, Iron-Based Catalysts. Energy Fuels 1994, 8, 117-123. (15) Font, J.; Moros, A.; Fabregat, A.; Salvado´, J.; Giralt, F. Influence of Fe and FeMo High Loading Supported Catalysts on the Coprocessing of Two Spanish Lignites with a Vacuum Residue. Fuel Process. Technol. 1994, 37, 163-173. (16) Bengoa, C.; Font, J.; Moros, A.; Fabregat, A.; Giralt, F. Influence des Catalyseurs He´te´roge`nes sur le Coprocessing d’un Lignite du Bergueda` avec un Re´sidu de Distillation sous Vide. Rev. Inst. Fr. Pet., submitted.
© 1996 American Chemical Society
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Energy & Fuels, Vol. 10, No. 3, 1996
Bengoa et al.
Table 1. Analysis of the Bergueda` Lignite original lignite
demineralized lignite
moisture ash fixed carbon volatile matter
Proximate Analysisa (wt %) 10.2 48.5 13.9 27.4
0.1 4.8 57.5 37.6
carbon hydrogen nitrogen sulfur H/C molar ratio
Ultimate Analysisa (wt %) 38.0 2.6 1.1 5.1 0.8
36.8 2.8 0.8 5.2 0.9
vitrinite liptinite inertinite aAs
Petrographic Analysis (wt % daf) 53.5 57.1 6.9 0.5 39.6 42.4
received.
lysts and reduces mechanical and handling difficulties.17 However, the presence of pyrite could lead to significant coal conversions in the absence of any external catalyst18 despite the unsatisfactory quality of the final products.19 Several studies using demineralized coal can be found in the literature. For example, the use of a demineralized, low-rank coal yielded higher conversions with moderate reaction times.20 A two-stage coal liquefaction process using deashed Australian brown coal has also been reported10 to yield larger oil production with less gas production. Another study, however, did not report significant differences from a comparison of original and demineralized coal.21 These differences in the results and conclusions may be due to modifications in the coal structure caused by the demineralization stage.22 The purpose of this study is to determine the effects of both supported Fe-based catalysts and commercial hydroprocessing catalysts on the coprocessing of a demineralized Catalan lignite with a vacuum residue. The same catalysts were tested in a previous study using untreated lignite.16 Experimental Section Materials. The coal used in this study is the lignite from the Bergueda` (Catalonia, Spain). This lignite is characterized by high levels of both ash and sulfur, being unsuitable for conventional combustion applications. Table 1 shows the proximate, ultimate, and petrographic coal analyses before and after the demineralization stage, which consisted of successive acid attacks on the coal with highly concentrated fluorhydric and chlorhydric acids.23 This treatment reduced the mineral matter content by a factor of 10. Small losses of volatile matter (17) Winschel, R. A.; Burke, F. P. Oil Agglomeration as a Pretreatment for Coal Liquefaction. Fuel 1987, 66, 851-858. (18) Snape, C. E. Similarities and Differences of Coal Reactivity in Liquefaction and Pyrolisis. Fuel 1991, 70, 285-288. (19) Curtis, C. W.; Tsai, K. J.; Guin, J. A. Catalytic Coprocessing: Effect of Catalyst Type and Sequencing. Ind. Eng. Chem. Res. 1987, 26, 12-18. (20) Snape, C. E. Characterisation of Organic Coal Structure for Liquefaction. Fuel Process. Technol. 1990, 15, 257-279. (21) Parker, R. J.; Fong, D. T.; Heck G. L. Agglomeration and Coprocessing of Alberta Subbituminous Coal. Fuel Process. Technol. 1990, 24, 231-236. (22) Andre`s-Besson, M.; Charcosset, H. Me´canismes, Cine´tique et Catalyse de la Lique´faction du Charbon par Hydroge´nation Sous Pression. Synthe`se Bibliographique. Deuxie`me Partie. Rev. Inst. Fr. Pet. 1984, 39, 365-382. (23) Von Radmacher, W.; Mohrhauer, P. Die Direkte Bestimmung des Mineralstoffgehaltes von Steinkohlen. Brennst. Chem. 1955, 15/ 16, Bd. 36, 236-239.
and minor differences in the percentages of C, H, N, and S were observed. The major characteristics of the vacuum residue used have been reported elsewhere.24 Table 2 lists the catalysts used and their characteristics. The catalysts made in the laboratory were impregnated by the dry soaking method.24 Reaction Setup. The tests were conducted in a 300 cm3 high pressure autoclave in which the samples were magnetically stirred and the tests operated in batches. In all experiments, the reactor loading was 45 g of vacuum residue, 11.25 g of demineralized lignite, and 2.25 g of catalyst when used. Once loaded, the reactor was filled with hydrogen at 12 MPa measured at room temperature. The reaction temperature was always set at 380 °C, and the reaction time was 1 h. The experimental procedure is described in more detail elsewhere.24 Product Analysis. The gases (GAS) produced were analyzed by gas chromatography, identifying H2, CO, CO2, H2S, and the hydrocarbons CH4, C2H6, and C3H8. The solid and liquid products were separated by Soxhlet extraction into three fractions denoted as insoluble organic matter (IOM), asphaltenes (ASP), and oils (OIL) using toluene and hexane as solvents. The IOM fraction does not include ash from the coal. Oils were further separated by open column adsorption chromatography into paraffin, aromatic, and polar subfractions using alumina and silica as adsorbents and hexane, toluene, and tetrahydrofuran as solvents. More specific information about the above analytical techniques is available in the literature.15,16,24-26
Results and Discussion The results will be discussed in terms of coal conversion
Xcoal )
IOMi - IOMf × 100 IOMi
and production of oils
Xoils )
OILf - OILi × 100 IOMi + ASFi
The subscripts i and f denote initial and final conditions, respectively. Table 3 includes the product distribution obtained for all the catalysts used. The corresponding coal conversions are plotted in Figure 1. Results show that the percentage of iron in the catalysts does not considerably modify the coal conversion reached. Furthermore, Xcoal seems to decline for Fe-loadings larger than 10%. This decrease is related to the high reduction in both surface area and pore size of the catalyst when iron loadings are increased. The availability of catalyst pores that large coal fragments may diffuse through is one of the critical steps in the performance of most catalysts in coprocessing.27 In addition, the catalytic activity of iron (24) Font, J.; Fabregat, A.; Salvado´, J.; Moros, A.; Bengoa, C.; Giralt, F. Influence of Temperature and Hydrogen Partial Pressure on the Coprocessing of Two Spanish Lignites with a Vacuum Residue. Fuel 1992, 71, 1169-1175. (25) Fabregat, A.; Salvado´, J.; Giralt, J.; Moros, A.; Font, J.; Giralt, F. Influence of Temperature, Catalysts and Partial Pressure of Hydrogen on the Coprocessing of Spanish Lignites. Int. J. Energy Res. 1994, 18, 317-328. (26) Bengoa, C.; Font, J.; Moros, A.; Fabregat, A.; Giralt, F. Coprocessing of the Bergueda` Lignite with a Vacuum Residue Under Increasing Hydrogen Pressure. Comparison with Hydrotreating. Fuel 1995, 74, 1704-1708. (27) Curtis, C. W.; Tsai, K. J.; Guin, J. A. Evaluation of Process Parameters for Combined Processing of Coal with Heavy Crudes and Residua. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 1259-1266.
Demineralized Catalan Lignite
Energy & Fuels, Vol. 10, No. 3, 1996 681 Table 2. Characteristics of Catalystsa
catalyst denomination active metal
γ-alumina
Fe-6 Fe(6%)
Fe-10 Fe(10%)
Fe-18 Fe(18%)
Fe-25 Fe(25%)
surface area (m2/g) average pore diameter (Å) total pore volume (cm3/g)
205 111 0.57
191 109 0.52
186 103 0.48
182 94 0.43
170 92 0.36
Fe-Mo Fe(25%) Mo(10%) 136 91 0.31
Co-Mo Co(15%) Mo(3%) 230 80 0.46
Ni-Mo Ni(3%) Mo(14%) 175 118 0.51
a Ni-Mo catalyst: Haldor Topsøe A/S Model TK-551. Co-Mo catalyst: ICI Catalysts Model 41-6. All catalysts are in sulfide chemical form and with a size of 25-50 mesh.
Table 3. Product Distribution catalyst IOM (g) asphaltenes (g) oils (g) gasesb (g) a
NRa
none
Al2O3
Fe-6
Fe-10
Fe-18
Fe-25
Fe-Mo
Co-Mo
Ni-Mo
ash
10.7 6.9 38.1
6.0 9.7 38.6 1.7
6.5 8.9 38.0 2.6
5.4 8.9 39.5 2.3
5.1 9.2 39.2 2.5
5.4 9.0 39.7 1.9
5.5 8.8 39.9 1.9
4.4 8.9 41.5 1.8
4.5 7.5 42.5 1.9
4.7 6.6 42.3 2.9
6.1 9.2 38.7 2.0
Initial loading, no reaction. b Produced gases, hydrogen not included.
Figure 1. Effect of the catalyst on coal conversion.
seems to be restricted to the cleavage of carbon-carbon bonds producing radicals, and a second metal to hydrogenize the radicals produced is needed. Otherwise, the radicals produced condense into heavy compounds that are collected in the IOM fraction. Thus, the use of bimodal catalysts should enhance coal conversion. This agrees with the results obtained with the Fe-Mo, CoMo, and Ni-Mo catalysts. This improved behavior of the bimodal catalysts including molybdenum agrees with previous studies,19,27-30 confirming the beneficial doping effect of this metal on the liquefaction and coprocessing reactions. The highest Xcoal is achieved for the Fe-Mo catalyst where both effects, carbon bond cleavage and stabilization of the radicals, are improved. For the Co-Mo and Ni-Mo catalysts, the lack of iron limits the extent of breakage of the coal structure and slightly lower conversions are obtained. Both catalysts, however, improve the coal conversions obtained without catalyst or with alumina. The ash resulting from calcination of the lignite does not produce any significant effect, suggesting that the catalytic activity shown by the mineral matter in previous studies16 is probably due to the intrinsic relationship between that mineral matter and the carbonaceous material in the coal structure. (28) Tischer, R. E.; Narain, N. K.; Stiegel, G. J.; Cillo, D. L. LargePore Ni-Mo/Al2O3 Catalysts for Coal-Liquids Upgrading. J. Catal. 1985, 95, 406-413. (29) Speight, J. G.; Moschopedis, S. E. The Co-processing of Coal with Heavy Feedstocks Fuel Process. Technol. 1986, 13, 215-232. (30) Bacaud, R. Evaluation of Catalytic Activity in Hydroliquefaction. Fuel Process. Technol. 1991, 28, 203-219.
Figure 2. Effect of the catalyst on production of oils.
Figure 2 shows the production of oils for all the catalysts tested. The hydrogenative capabilities of the bimodal catalysts are highest. They produce higher Xoils than the Fe catalysts do. The commercial Co-Mo and Ni-Mo catalysts are superior to those of Fe-Mo because they are more capable of transforming the asphaltenes into oils, despite the lower coal conversions attained. This may be due to the better structural characteristics (surface area and pore diameter) of these commercial catalysts. In general, the conversions into oils achieved with the demineralized lignite are much higher than those obtained with untreated lignite.16 This trend might be explained by the better performance of the catalysts in a reaction environment that is free from heavy poisoning metals. Also, the demineralization treatment affects the coal structure, leading to a deeper depolymerization that produces fragments that are smaller than those coming from untreated coal, which can be included in oils rather than in asphaltenes. Table 4 summarizes the composition of the oils produced. In all cases the percentage of aromatics falls with respect to the original percentage (57.0%) because the aromatics are progressively converted into paraffins. However, the final composition is greatly affected by the coal conversion attained, that is, by the catalyst used. Thus, for the oils produced by coprocessing with catalysts containing molybdenum, the percentage of paraffins is high probably because of the processes of sulfur removal by the opening of aromatic rings. The oils formed with Mo-containing catalyst tests show high
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Energy & Fuels, Vol. 10, No. 3, 1996
Bengoa et al. Table 4. Composition of Oils catalyst
subfraction (%)
NRa
none
Al2O3
Fe-6
Fe-10
Fe-18
Fe-25
Fe-Mo
Co-Mo
Ni-Mo
ash
paraffinic aromatic polar
29.7 57.0 13.4
37.7 43.7 18.6
38.2 39.6 22.2
38.1 38.4 23.5
37.1 42.5 20.4
37.3 42.7 20.0
37.7 42.7 19.6
39.8 41.8 18.4
39.4 41.9 18.7
42.2 42.5 15.3
41.4 42.1 16.5
a
Initial loading, no reaction. Table 5. Composition of Gases Produced catalyst
gases (g)
none
Al2O3
Fe-6
Fe-10
CO CO2 H2S
0.1 0.2 1.1
0.1 0.2 1.8
0.1 0.2 1.6
0.1 0.2 1.8
CH4 C2H6 C3H8
0.2 0.1
0.3 0.1 0.1
0.2 0.1 0.1
0.2 0.1 0.1
Fe-18
Fe-25
nonhydrocarbons 0.1 0.1 0.1 0.2 1.4 1.2 hydrocarbons 0.3 0.1 0.1
0.2 0.1 0.1
Fe-Mo
Co-Mo
Ni-Mo
ash
0.1 0.2 1.1
0.1 1.4
0.1 2.3
0.1 0.1 1.4
0.2 0.1 0.1
0.2 0.1 0.1
0.3 0.1 0.1
0.2 0.1 0.1
Table 6. Ultimate Analysis of Oils catalyst element (%)
NRa
none
Al2O3
Fe-6
Fe-10
Fe-18
Fe-25
Fe-Mo
Co-Mo
Ni-Mo
ash
carbon hydrogen nitrogen sulfur
85.8 10.9 0.5 2.7
84.6 10.7 0.5 2.5
85.4 10.9 0.5 2.3
85.4 10.9 0.5 2.3
85.3 10.7 0.5 2.3
84.9 10.8 0.5 2.4
84.4 10.7 0.5 2.5
84.7 10.8 0.5 2.4
85.4 11.0 0.5 1.6
85.9 11.2 0.5 1.2
85.8 10.9 0.5 2.4
a
Initial loading, no reaction. Table 7. Ultimate Analysis of Asphaltenes catalyst
element (%)
NRa
none
Al2O3
Fe-6
Fe-10
Fe-18
Fe-25
Fe-Mo
Co-Mo
Ni-Mo
ash
carbon hydrogen nitrogen sulfur
84.3 7.5 1.5 5.7
83.9 6.4 1.5 5.2
85.6 6.2 1.5 4.8
85.2 6.6 1.5 5.0
85.6 6.3 1.5 4.9
83.4 7.5 1.7 4.6
84.7 6.4 1.4 5.1
84.1 7.4 1.7 4.2
84.0 6.6 1.7 4.0
83.9 6.6 1.7 3.8
85.0 5.9 2.0 4.5
a
Initial loading, no reaction.
sulfur removal and a low percentage of polar compounds, especially in the case of the Ni-Mo catalyst, which has the lowest level. Table 5 shows the composition of the gases produced. In general, the production of hydrocarbon gases is lower than that reported for the coprocessing of untreated lignite.16 This trend has been reported elsewhere,10 and it is probably related to the loss of volatile matter during the demineralizing treatment. Note that the volatile matter is mostly formed by low molecular weight organic compounds weakly linked to the aromatic structure of the coal. Nevertheless, the lower production of gases as a result of using Fe catalysts has been also reported.31 As far as this is concerned, the production of hydrocarbon gases proves to be rather insensitive to the presence of a catalyst. For the production of nonhydrocarbon gases, the production of CO and CO2 is approximately constant for all catalysts, while the production of H2S peaks for the Ni-Mo catalyst, in accordance with the low percentage of polar compounds observed in the corresponding oil fraction. This suggests that the Ni-Mo catalyst is the most effective for desulfuration, as is also suggested by the elemental analysis of the oils and asphaltenes given in Tables 6 and 7, respectively. The degree of desulfuration achieved (31) Oelert, H. H. State of the Art of the Coprocessing. Review Contract No. EN3V-0025-D(N); European Commission: Brussels, 1987.
Figure 3. Effect of the catalyst on consumption of hydrogen.
with the Ni-Mo catalyst is twice that observed for other catalysts. On the other hand, no conclusion can be drawn for the hydrogen sulfide production because it is impossible to discern the exact source of sulfur, coal, or sulfided form of the catalytic metals. Finally, it should also be noticed from Tables 6 and 7 that no catalyst denitrogenates the products, at least for the present mild operation conditions. Figure 3 illustrates the consumption of hydrogen. Once again, the Mo-containing catalysts give the highest uptakes, in agreement with the larger coal conversion and production of oils obtained with them. It must be
Demineralized Catalan Lignite
Energy & Fuels, Vol. 10, No. 3, 1996 683 Table 8. Some Characteristics of Products catalyst
oils (MW) asphaltenes (MW) aromatic Hb (%) a
NRa
none
Al2O3
Fe-6
Fe-10
Fe-18
Fe-25
Fe-Mo
Co-Mo
Ni-Mo
ash
910 1200 8.0
390 1380 11.5
360 1040 12.1
420 1100 10.8
440 1270 11.6
530 1200 14.0
490 1150 15.5
520 1250 15.5
430 1220 18.3
450 1280 16.1
410 960 9.0
Initial loading, no reaction. b In the aromatic subfraction of the oils.
noted that about 35% of the hydrogen uptake can be attributed to the formation of hydrogen sulfide in the least favorable case of the Fe-10 catalyst. This has to be taken into account because, even though desulfuration of the products is one of the goals of any upgrading treatment, the greater demand for highly expensive hydrogen could offset the benefits of obtaining products with a lower sulfur content. The average molecular weights (MW) for both the oils and the asphaltenes are summarized in Table 8, which also includes the percentage of aromatic hydrogen in the aromatic subfractions. In all cases, the MWs for both the resulting oils and the asphaltenes are lower than those obtained from untreated lignite,15 confirming the greater breaking of structures in the demineralized coal tests. In particular, the MWs of the asphaltenes are very similar for all catalysts, except in the test with no catalyst, where the MW is slightly higher, suggesting that the absence of a catalyst produces heavier coal fragments. The same results can be observed for the MW of the oils, where the values are equal for all catalysts. What is more, in the tests where a high production of oils is observed, the percentage of aromatic hydrogen in the aromatic compounds seems to increase. This may suggest that the structure of the oils is more condensed in these tests. Moreover, in comparison with the original lignite,16 there is more aromatic hydrogen in the aromatic subfraction. This again suggests some depolymerization of the coal structure, i.e., breaking of lateral aliphatic chains, during the demineralization. Finally, Figure 4 shows the chain length distribution of the paraffins. The distribution does not seem to depend on the catalyst, although paraffins from commercial catalysts tend to be heavier. This may be due to the greater ability of Mo commercial catalysts to hydrogenate and condense heavy aromatic compounds. Moreover, the overall percentage of chains longer than 24 carbons is about 40%, whereas for untreated lignite, it was about 70%.16 This is one more confirmation of the deeper fragmentation of the coal structure during the demineralization. Conclusions A set of Fe-supported catalysts and two Co-Mo and Ni-Mo commercial catalysts have been evaluated for
Figure 4. Effect of the catalyst on chain length distribution of the paraffin subfraction.
the coprocessing of a demineralized lignite from the Bergueda` with a vacuum residue. The demineralization procedure removes over 90% of the original mineral matter of the lignite. However, the treatment also causes structural changes in the coal and it is difficult to compare present results with those obtained elsewhere for the untreated lignite. All catalysts tested improve both coal conversion and production of oils. The percentage of iron does not affect significantly these results, suggesting that, in this case, their performance is altered, possibly because of a too small pore size. The Fe-based catalysts seem to improve the breaking of the coal structure but are unable to stabilize the fragments, which condense into heavy products. The presence of molybdenum as a doping metal also largely enhances the coal conversion and the production of oils. The commercial Co-Mo and Ni-Mo catalysts perform well in the production of oils because of their ability to upgrade asphaltenes. These commercial catalysts also have a significant desulfuration activity, which yields liquid products with a lower sulfur content and gases rich in hydrogen sulfide. Acknowledgment. This work was supported by the Spanish Government, Programa Sectorial de Promocio´n General del Conocimiento (Contract No. PB88-0217). We thank Mr. Josep M. Borra´s for his technical assessment in conditioning the analytical methods. EF950146X
