996
Energy & Fuels 1996, 10, 996-1000
Utilization of Petroleum Waste in Coal Liquefaction Prakash K. Ramdoss, Chin-Hsian Kuo, and Arthur R. Tarrer* Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849 Received January 17, 1996. Revised Manuscript Received April 3, 1996X
Coprocessing of coal with a petroleum waste containing grease in waste oil was studied. Experimental parameters such as temperature, pressure, reaction time, coal loading, and grease loading in the system were examined. Coal conversions were found to increase with temperature, hydrogen pressure, reaction time, and coal loading. Coal conversions in excess of 90% were obtained during coprocessing, with conversions to oil of over 50%. At a fixed coal loading, the presence of a higher amount of grease in the system was found to increase the conversion of coal. This can be explained as due to the catalytic action of the heavy metals such as molybdenum in the grease during coprocessing. The high aromaticity of waste grease made it a good solvent for coal liquefaction. The waste oil and waste grease were demetalized during coprocessing, and the viscosity of the oil was reduced.
Introduction Annually, over a million tons of waste grease and about 1.2 billion gallons of waste oil are generated in the United States.1 With the increasingly stringent EPA regulations, disposal of waste grease and waste oil is becoming more and more difficult. Some cement kilns do not even accept waste grease because of its sticky nature which causes handling problems. A number of remediation techniquessphysical, chemical, thermal, and biologicalsare available for treating petroleum wastes like waste grease and waste oil. However, all of these techniques have certain limitations. Although the biological treatment of petroleum wastes2 is economical, it is an extremely slow process. It also does not recover the useful part of the waste material and sometimes emits toxic vapors. Moreover, the technique has been found to fail when loading of the waste materials is high. Thermal techniques such as incineration are effective but are very expensive. Moreover, due to stringent environmental regulations concerning air emissions, their use has raised concerns. Chemical stabilization is another method for the disposal of petroleum waste. Here, the volume of the toxic substrate is increased by diluting it with a binding material but useful material is not recovered from the waste. At present, most of the waste grease is disposed through landfilling. Due to the recent ban on landfilling of these waste materials, this method of disposal cannot be used extensively. Hence, the need arises for exploring other disposal techniques. Recently, more researchers have become interested in coprocessing coal with waste materials such as used tires, waste plastics, and waste oil. The present emphasis in coal liquefaction is to coprocess coal with these waste materials and to improve the economics of coal liquefaction. Coprocessing coal with waste oil has been studied by Sanjay et al.1 Coprocessing of petroleum Abstract published in Advance ACS Abstracts, May 1, 1996. (1) Sanjay, H. G.; Tarrer, A. R.; Marks, C. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1993, 38 (1), 131. (2) Michael P.; Sambasivam, Y. Environ. Prog. 1993, 12, 1. X
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residue with coal was studied by Costi et al. in 1987.3 Yan et al.4 concluded from their study that liquefaction of coal in the presence of petroleum fractions increased fuel oil production. Coprocessing coal with scrap tires has been studied by Liu et al. in 1994.5 Coal conversions of up to 56% were obtained using shredded tires. Studies by Farcasiu6 indicated that the presence of carbon black improved the quality and quantity of the products. It has also been found that catalysts such as iron oxide improve the conversion of coal to useful oil during coprocessing.7,12 The addition of small amounts of sulfur to the system improves the selectivity of the process.8 Researchers at UOP Inc.11 have studied the feasibility of coprocessing coal with heavy residual oils, a UOP vanadium-based catalyst was used for the study. A molybdenum-based catalyst was also developed and evaluated on a bench scale. Waste oil was found to be a good solvent for coal coprocessing.12 The benefits of coprocessing waste materials with coal are reduced cost of liquefaction and simultaneous disposal of waste materials. Coprocessing of coal with waste grease and waste oil converts the waste materials into useful products. Moreover, the viscosity of the waste oil was found to decrease to a great extent after coprocessing. Hydrocracking and thermal cracking take place during coprocessing, resulting in a decrease in the viscosity of the feed materials. The waste oil and waste grease generated pose an environmental hazard as they contain metallic compounds and sulfur. These materials must be re-refined (3) Costi A. A.; Yan, T.-Y. Ind. Eng. Chem. Res. 1987, 26, 12. (4) Yan, T. Y.; Espenscheid, W. Fuel Process. Technol. 1983, 7, 121. (5) Liu, Z.; Zondlo, J. W.; Dadyburjor, D. B. Energy Fuels 1994, 8, 3. (6) Farcasiu, M.; Smith, C. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1992, 37 (1), 472. (7) Suzuki, T.; Yamada, O.; Fujita, K.; Takegami, Y.; Watanabe, Y. Chem Lett. 1992, 1467-1468. (8) Marriadassou, D. G.; Charcosset, H.; Andres, M.; Chiche, P. Fuel 1983, 62. (9) Tanabe, K.; Hattori, H.; Yamaguchi, T.; Iizuka, T.; Matzuhashi, H. Fuel Process. Technol. 1986, 14, 247. (10) Pradhan, V. R.; Tierney, J. W.; Wender, I.; Huffman, G. P. Energy Fuels 1991, 5, 497. (11) Haggin, J. Chem. Eng. News 1992, 20 (April), 34. (12) Sanjay, H. G.; Tarrer, A. R.; Marks, C. Ind. Eng. Chem. Res. 1994, 15, 4.
© 1996 American Chemical Society
Use of Petroleum Waste in Coal Liquefaction
Energy & Fuels, Vol. 10, No. 4, 1996 997
Table 1. Properties of Sample Bank Waste Oil A specific gravity sulfur (wt %) water (wt %) ash (wt %)
0.888 1.01
