Energy & Fuels 1995,9, 319-323
319
Influence of the Porous Texture of Coals on Their Hydrogenation Processes Catalyzed by Fe Jose Rivera-Utrilla," Francisco J. Maldonado-Hbdar, Ana M. Mastra1,t and M. C. Mayoral? Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain, and Instituto de Carboquimica, CSIC, Apdo 589, 50080 Zaragoza, Spain Received August IO, 1994@
Nine coals from Spanish, British, German, and American mining basins were hydrogenated using Fe catalyst precursors (red mud and FeS04), without solvent a t 300,350,and 400 "C and 10 MPa of H2. Overall conversion and product distribution are related to the textural characteristics of the original coals and are studied throughout the distinct hydrogenation processes. Results reveal that with FeS04 as a catalyst precursor, conversions increase with coal surface area. However, when red mud (RM) is used, conversions are independent of coal textural characteristics. Higher conversions are obtained with FeS04 than with RM at 300 and 350 "C whereas at 400 "C higher conversions are obtained with RM. This different catalytic activity is also reflected in the changes of the textural characteristics observed in each case. Up to 350 "C, the residues from FeS04-catalyzed processes reveal increased microporosity destruction and a greater increase in meso- and macropore volume. At 400 "C, however, both these effects are greater for RM.
Introduction The role and importance of catalysts on direct coal liquefaction have been deeply studied. The addition of an active catalyst enhances net conversion and selectivity (increases oil yield, the most valuable conversion product) and leads t o a more efficient hydrogen consumption and less severe processing conditions. The kind of catalyst t o use, however, is a matter of contention. Commercial supported metal catalysts (e.g., Co-Mo/ A1203 or Ni-Mo/AlzOa) can have poor contact with the coal and are very expensive, and sophisticated techniques are required for catalyst recovery. Unsupported dispersed catalysts however, are often in closer contact with the coa1.l However, if low surface area solids are used, a high catalyst concentration is required, e.g., pyrite was found to be effective in concentrations of several weight percent.2 One method of increasing dispersion is to introduce the catalyst as a soluble or volatile precursor. Molybdenum has been used for many years as an effective catalyst for coal liquefaction, hydrodesulfurization and hydrocracking p r o c e ~ s e s . ~Other - ~ catalytic precursors, e.g., nickel acetate: have also been used but these are often expensive. Cheaper alternatives with good results are provided by some Fe salts, such as
* Author to whom correspondence should be addressed.
Instituto de Carboquimica. Abstract published in Advance ACS Abstracts, February 15,1995. (1)Herrick, D. E.; Tierney, J. W.; Wender, I.; Huffman, G. P.; Huggins, F. E. Energy Fuels 1990,4,231-36. (2)Garg, D.;Givens, E. Ind. Eng. Chem. Process Des. Dev. 1982, +
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21, 113. (3)Garcia, A. B.;Schobert, H. H. Fuel 1989,68, 1613. (4)Mastral, A. M.; Rubio, B. Fuel 1989,68, 80.
(5)Maldonado-H6dar, F. J.; Rivera-Utrilla, J.; Mastral, A,; Izquierdo, MT. Fuel, in press. (6)Takemura, Y.; Okada, K. Fuel 1988,67, 1548.
Fe(C0)5 and FeS04,117 and also disposable catalysts, such as red mud (RM) or other iron oxide containing products;8 these are also advantageous in that they do not need to be recovered. In the literature, many papers focus on the influence of chemical and porous properties of the supported catalyst on the hydrogenation of distillate products from coal liquefa~tion.~-l~ There is, however, a lack of information about the influence of the porous texture of coals on their catalyzed hydrogenation proce~ses.~ The aim of this work is therefore to study the influence of coal porous texture on the hydrogenation processes catalyzed by Fe from two catalyst precursors, FeS04 and red mud (RM). Moreover, the modifications of the coal porous texture during the hydrogenation processes are also studied to increase our knowledge of the mechanism and development of the reaction.
Experimental Section In a previous paper,13 the chemical and textural characteristics of 23 coals from different mining areas around the world were studied. Nine of them were selected for this study. Their proximate analysis is shown in Table 1. Some of the most important textural parameters are also included in this table (S(C02)and S(N2) are the surface areas determined from COz and Nz adsorption isotherms respectively; VZ is the pore volume contained in pores in the diameter range 3.7-50 nm; V3 is the pore volume contained in pores in the diameter range (7)Suzuki, T.; Yamada, 0.; Takehaski, Y.; Watanable, Y. Fuel Process. Technol. 1986,10, 33-43. (8) Mastral, A. M.; Mayoral, M. C.; Palacios, J. M. Energy Fuels, 1994,8,94. (9)Song, C . ; Hanaoka, K.; Nomura, M. Energy Fuels 1992,6,619. (10) Masuyama, T.; Kageyama, Y.; Kawai, S. Fuel 1990,69,245. (11)Krichko. A. A.: Maloletnev. 0.:Mau. A.: Slivinskava. " , J. J.: Jacobaen, A. C.; Christensen, H. Fuel 1990, 69,344. (12)Song, C.;Nihonmatsu, T.; Nomura, M. Ind. Eng. Chem. Res. 1991. _ _ _ _, 30. 1727. (13)Rivera-Utrilla, J.; Ferro-Garcia, M. A.; Maldonado-Hodar, F. J.; Mastral, A. M. Coal Qual., in press.
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0887-0624/95/2509-0319$09.00/0 0 1995 American Chemical Society
Rivera-Utrilla et al.
320 Energy & Fuels, Vol. 9, No. 2, 1995 Table 1. Proximate Analysis and Textural Characteristics of Coals"
MS9 MS13 MS16 MS18 MB19 MS20 MB22 MB23 MB25
subbit. C subbit. C subbit. C subbit. C HVC bit. ligniteA MV bit. LV bit. HVC bit.
31.1 23.5 21.6 27.5 17.8 64.1 12.2 11.5 13.2
41.0 35.5 33.9 33.1 32.7 24.5 26.2 17.1 39.5
27.9 41.0 44.5 39.4 49.5 11.5 61.6 71.4 47.3
129 202 160 196 159 195 138 124 181
10.2 5.0 11.2 4.7 9.3 4.8 2.9 3.0 10.4
0.054 0.004 0.042 0.028 0.016 0.026 0.000 0.000 0.000
0.028 0.028 0.020 0.023 0.015 0.051 0.005 0.008 0.011
1.35 1.47 1.49 1.58 1.37 1.42 1.35 1.32 1.40
a S(CO2) = surface area obtained by COz adsorption a t 273 K. S(N2)= surface area obtained by Nz adsorption at 77 K. Vz = volume of pores with diameter between 3.7 and 50 nm, obtained by mercury porosimetry. V3 = volume of pores with diameter between 50 and 200 nm, obtained by mercury porosimetry. @He = Helium density at room temperature.
50-200 nm; P is the porosity corresponding to pores
