Energy & Fuels 1999, 13, 895-902
895
Solvent Effect on the Extraction of Beypazari Oil Shale Nuray Olukcu,† Jale Yanik,*,‡ Mehmet Saglam, Mithat Yuksel, and Musa Karaduman Petrochem. Techn., Dokuz Eylul University, IMYO, 35150 Izmir, Turkey Received December 15, 1998. Revised Manuscript Received March 18, 1999
Beypazari oil shale was subjected to supercritical fluid extraction with water and toluene separately. Considerable differences were observed in the yields (wt %) and compositions of the oils obtained from oil shale SCW (supercritical water) gave a higher conversion degree of kerogen in oil shale than SCT (supercritical toluene), whereas oil yield in SCT was 41% more than that in SCW. Oils having more asphaltenic and polar compounds were obtained from SCW. Although the polar contents decreased in SCT oils with increasing temperature, they increased in SCW oils. No n-alkenes-1 were observed in the aliphatic fraction of SCW extraction oil. The temperature affected the isomerization of aliphatics in SCT oils. The molecular weight of oils was affected basically by the temperature at both supercritical fluids.
Introduction Recently, considerable interest has been expressed in the extraction of solid fuels such as coal and oil shale using supercritical fluids such as common organic solvents and water. As pointed out by Kershaw1 supercritical fluid has the following major rules: (1) the supercritical fluid extracts the products from pyrolysis of coal, (2) the supercritical fluid extracts smaller molecules which are not bound to the coal matrix, (3) the supercritical solvent reacts with the coal structure. In the first two cases, extraction yield would depend predominantly on the solvent density at the extraction conditions. In the third case, the structure of the solvent is crucial and the chemical reactions are still not well understood. Deshpande et al.2 found that supercritical water acts not only as a solvent but as a reactant in the conversion of coal to gases and liquids. Model and co-workers3,4 studied supercritical water extraction of glucose, cellulose, maple sawdust, and coal slurries. They showed that water acts also as a reforming reactant. Houser et al.5 found that supercritical water is an active participant in the decomposition of organic compounds. Funazukiri et al.6 studied supercritical fluid extraction of Chinese oil shale and it was found that polar components were more easily decomposed by SCW than by supercritical toluene (SCT). The yield of nonpolar components was not affected by the solvents water and * Author to whom correspondence should be addressed. † E-mail:
[email protected]. ‡ Current address: Department of Chemistry, Ege University, 35100 Izmir, Turkey. E-mail:
[email protected]. (1) Kershaw, J. R. Fuel 1997, 76 (5), 453-54. (2) Despande, V. G.; Holder, G. D.; Bishop, A. A.; Gopal, J. Fuel 1984, 63, 956. (3) Modell, M. Gasification and Liquefaction of Forest Products in Supercritical Water. AlChe 89th National Meeting, Oregon, 1980. (4) Modell, M.; Reid, R. C.; Amin, S. I. U.S. Patent 4,113,446, 1978. (5) Houser, T. J.; Tiffany, D. M.; Li, Z.; McCarville, M. E.; Houghton, M. E. Fuel 1986, 65, 827. (6) Funazukuri, T.; Yokoi, S.; Wakao, N. Fuel 1988, 67, 1510.
toluene. Berkowitz et al.7 showed that under near critical conditions water can promote a variety of thermally driven homolytic and/or hydrolytic bond scissions. Canel8 studied liquefaction of two Turkish lignites and an oil shale with water in sub- and supercritical states. It was obvious that the conversion degree and the extract yield also depended on the chemical composition of the solid fuel. For both lignites and oil shale, supercritical water is sufficient to obtain a high conversion degree and high extract yield whereas the higher oil yield from oil shale was obtained at subcritical pressure. Haoquan and coworkers 9 conducted a series of experiments in which lignite was extracted with water in sub- and supercritical states to investigate the effect of temperature on extract formation rate, extract yields, and product components at different pressures. They obtained high conversion and extract yields by using SCW extraction. They noted that at subcritical pressure the main fraction of extract was oil and at supercritical pressure it was preasphaltene. Toluene is also one of the most commonly examined solvents for supercritical extraction, applied to carbonaceous materials in order to obtain liquid fuels. Rober M.Baldwin et al.10 showed that supercritical toluene did not act as a reactant but caused significant change on the stabilization mechanism of volatile materials in their studies with oil shales. Thus, they determined that SCT increased the conversion degree and hydropyrolysis products yield. In the same study, the presence of hydrogen in toluene increased the yield of aromatics while minimally affecting the yield of aliphatics. In a study11 of thermochemical reactions in subcritical and supercritical toluene with Israeli Mishor Rotem oil (7) Berkowitz, N.; Calderon, J. Fuel Process. Technol. 1990, 25, 33. (8) Canel, M.; Missal, P. Fuel 1994, 73 (11), 1776. (9) Hu, H.; Guo, S.; Hedden, K. Fuel Process. Technol. 1998, 53 (3), 269. (10) Baldwin, R. M.; Chen, W. K. Fuel 1987, 66, 353. (11) Yurum, Y.; Kramer, R.; Levy, M. Thermochim. Acta 1986, 105, 51.
10.1021/ef9802678 CCC: $18.00 © 1999 American Chemical Society Published on Web 05/07/1999
896 Energy & Fuels, Vol. 13, No. 4, 1999
Olukcu et al.
shale, it was shown that thermal events were absent during the supercritical interaction. Therefore it appears that the whole process occurred only in the heating period at subcritical conditions. It was observed that at supercritical conditions the material originally susceptible to solubilization and new material produced from thermolysis reactions were extracted from the kerogen. Guo Shu-Cai et al.12 studied supercritical toluene extraction of Chinese oil shale. The results indicate that supercritical extraction of oil shale with SCT can give up to twice the oil yield of that from conventional retorting. With supercritical hydroextraction, where an H-donor (tetralin) is added to the supercritical solvent, a complete recovery of the oil shales kerogen with high yield of liquid products is possible. The purpose of the present study is to examine the factors affecting conversion, extracts yield, and composition and also to discuss the extraction mechanism from the relationship among the oil composition, the solvent power of the supercritical fluid, and the reactions occurring during the extraction of oil shale. For this purpose, the Beypazari oil shale was subjected to suband supercritical water extractions and supercritical toluene extraction in a batch autoclave.
Table 1. Proximate and Ultimate Analysis of Beypazari Oil Shale proximate analysis (wt % air-dry basis) moisture 1.0 ash 68.0 fixed carbon 3.2 volatile matter 28.8 heating value (kcal/kg) 925
ultimate analysis (wt %, air-dry basis) C 12.9 H 1.0 S 1.5 N 0.3 O (difference) 16.3
Fischer assay analysis (wt %) shale oil 6.4 gas 1.1 water 0.7 residue 91.2
Scheme 1. Separation of SCW and SCT Extraction Products, Respectively
Experimental Section Oil shale samples from the Beypazari deposit were crushed to the desired particle size and stored under a N2 atmosphere. Analyses of the oil shale are given in Table 1. Extraction experiments were conducted in a 100 mL stainless steel shaking autoclave. The autoclave was charged with 30 g of oil shale and the required amount of water or toluene. A stream of N2 was introduced into the reactor to remove air. The autoclave was heated to the desired temperature at a rate of 5 K min-1 and was held at this temperature for the required duration. At the end of the reaction, the reactor was cooled by a fan system. After the gaseous products were vented, the reactor contents were filtered to separate solid and liquid parts. In water extraction the liquid part consists of two layerssaqueous and organic. The aqueous layer was separated from the organic one by use of a mixture of tetrahydrofuran (THF) and toluene (1/1) in a separating funnel. The residual solid was placed in a Soxhlet thimble and extracted for 8 h with THF. The Soxhlet extract was combined with the filtrate (or organic layer in water extraction). Solvent was stripped off by a rotary evaporation at
