Energy & Fuels 1990, 4, 146-151
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primary migration distance, m activation energy, cal/mol relative rate of coking or cracking of oil species fraction of lithostatic pressure for implied fracturing pressure-dependent factor for oil cracking rate rate constant (units of A in Table IV) equilibrium constant pressure coefficient of porosity, Pa-' effective hydraulic conductivity, m3 of fluid/ (m3 of reactor-Pad hydraulic conductivity coefficient, m3 of reactor/ (m3 of fluid.Pa.s) molecular weight, kg/mol molar concentration of gas, mol/m3 of reactor molar concentration of liquid, mol/m3 of reactor pore pressure, Pa hydrostatic pressure, Pa lithostatic pressure, Pa reaction rate, kg/(m3 of reactor-s) gas constant rate of fluid expulsion, m3of fluid/(m3 of reactor-s) temperature, K
temperature ("C)of maximum reaction rate molar volume of gas, m3/mol molar volume of liquid, m3/mol 5. V uncorrected molar volume, m3/mol W mass concentration, kg/m3 of reactor X mole fraction in liquid phase mole fraction in vapor phase Y z depth, m Greek Letters K intrinsic permeability, m2 P viscosity, Paas t porosity, m3 of pore volume/m3 of reactor 4 partial fugacity coefficient standard deviation of Gaussian activation energy "E distribution, cal/mol Superscripts B virtual bitumen G vapor phase K virtual kerogen L liquid phase S solid phase T,, VG
Effect of Water Vapor Pressure on the Dehydration and Dehydroxylation of Kaolinite and Smectite Isolated from Australian Tertiary Oil Shales John H.Levy CSIRO Division of Fuel Technology, Lucas Heights Research Laboratories, Private Mail Bag 7, Menai, New South Wales, Australia 2234 Received November 13, 1989. Revised Manuscript Received January 8, 1990
Dehydration and dehydroxylation of kaolinite isolated from Nagoorin oil shales and smectite from Rundle oil shales were studied by thermogravimetry in water vapor-nitrogen atmospheres. It was found that the dehydroxylation of Nagoorin kaolinite was similar to that of other kaolinites and that the metakaolinite product formed will not rehydroxylate under steam-retorting conditions. Dehydration and rehydration of Rundle smectite were similar to those of other montmorillonites although dehydroxylation occurred at much lower temperatures, due to iron substitution in the aluminosilicate lattice. Again, rehydroxylation will not occur under steam-retorting conditions. The effect of water vapor pressures, from 0 to 80 kPa, on the temperature of dehydroxylation of both clays has been defined and was similar for both. Increasing water vapor pressure significantly increased the dehydroxylation temperature while the temperature range of dehydroxylation was reduced. The temperature of dehydroxylation can be increased to values above those typical for retorting (500 "C)so that there is good potential for shifting these endothermic reactions from the retort to the combustor, resulting in decreased retort heat requirements and thus reduced ash recycle ratios.
Introduction Results of clay characterization studies' highlighted the importance of smectite and kaolinite in the Australian Tertiary oil shales and demonstrated that kaolinite isolated from Nagoorin oil shales and smectite from Rundle oil shales were representative of these clays. The Tertiary kaolinites appeared chemically and thermally similar to other kaolinites, but the smectites were members of the ~~
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(1)Patterson, J. H.; Hurst, H.J. Characterization of Clay Minerals in the Tertiary Oil Shales of Queensland, Australia. Proceedings of the 5th Australian Workshop on Oil Shale, Lucas Heights, Australia, December 7 , 8 , 1989 pp 189-194.
0SS1-0624/90/2504-0~46$02.50/0
montmorillonite/nontronite series with unusually low thermal stability. Because both these clays could well be partially dehydroxylated during retorting,'g2 more detailed studies of their endothermic reactions were needed. While it was known3 that the temperature of dehydroxylation would be increased at higher water vapor pressures, few data were available. For kaolinite, the effect of water vapor pressure was significant in isothermal ki(2) Patterson, J. H.;Hurst, H.J.; Levy, J. H.; Killingley, J. S. Processing Reactions of Minerals. Proceedings of the 5 t h Australian Workshop on Oil Shale, Lucas Heights, Australia, December 7,8,1989 pp 141-146. (3) Levy, J. H. Unpublished results.
0 1990 American Chemical Society
Kaolinite and Smectite from Tertiary Oil Shales
Energy & Fuels, Vol. 4, No. 2, 1990 147 bottom of the pan and heated at 10 OC min-' in a dynamic gas atmosphere flowing at 130 mL min-'. Gases used were either dry nitrogen or nitrogen containing water vapor, with water vapor pressures ranging from 10 to 80 kPa.
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Results and Discussion Nagoorin Kaolinite. Thermogravimetric (TG) curves for Nagoorin kaolinite and Georgia kaolinite are compared in Figure 1. The thermal properties of the Tertiary kaolinite broadly match those of Georgia kaolinite. After the initial loss of surface water up to 150 "C, there are three stages in the TG curves. The first is a long slow process of water loss up to about 400 "C, probably due to a diffusive loss of tightly bound water associated with the clays. The second stage arises from dehydroxylation, Le., loss of structural OH groups, which commences at about 400 "C, peaks at almost 500 "C, and is substantially completed by 545 "C under low water vapor pressures. Following this, further slow water loss occurred up to between 700 and 800 "C which is generally attributed to final ejection of OH groups from the metakaolinite mainly produced in the second stage. For the Nagoorin concentrate, the first and third stages will not be further explored because of the uncertainty arising from the initial and final stages of dehydroxylation of the smectite component. The second stage is dominated by the kaolinite, however, and the Nagoorin concentrate could be used to study the effects of water vapor pressure on dehydroxylation. Effect of Water Vapor Pressure on Dehydroxylation. TG and DTG curves were recorded for Nagoorin kaolinite a t 0, 10,20,40, and 80 kPa water vapor pressure and are shown in Figure 2. The temperature of dehydroxylation increased substantially as the water vapor pressure increased. The temperature range over which dehydroxylation occurred was also significantly reduced. The DTG curves (Figure 2) show these important effects most clearly and reveal the disproportionate effects at low water vapor pressures. Differences between the DTG curves at 0 and 10 kPa are very striking. The peak temperature increased from 498 to 530 "C and the temperature range decreased from 125 to 100 "C. Peak temperatures continued to increase at higher vapor pressures, whereas the dehydroxylation range remained much the same. This relationship between peak temperature and water vapor pressure is displayed in Figure 3. It can be seen that the increase was almost linear up to 40 kPa. Pressures to 80 kPa increased the peak temperature but at a much slower rate. These results show that the temperature of kaolinite dehydroxylation can be increased by up to 90 "C at a water vapor pressure of 40 kPa, at typical retorting temperatures of 500 "C. This accounts for differences in the extent of decompositionllof kaolinite between modified Fisher assay (MFA) and process development unit (PDU) retorting. Although MFA water vapor pressures are unknown, they are probably higher than in the fluidized-bed PDU. These results show good potential for minimization of this endothermic reaction in retorting. This is particularly significant for the Tertiary oil shales containing' the most kaolinite, i.e., those from the Condor, Lowmead, Duaringa, Nagoorin South, and Nagoorin deposits. Rehydroxylation of Metakaolinite. If kaolinite is not dehydroxylated in the retort, then it probably will be in the combustor. It is important to know if rehydroxylation occurs when the combusted shales are recycled to the retort under steam-retorting conditions. Published datal2 in-
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Figure 1. T G curves for Nagoorin and Georgia kaolinites.
netic studies4 and in very high pressure differential thermal analysis ~ t u d i e s . ~No similar studies were found for montmorillonite or other smectites, but for montmorillonite, prior derivative thermogravimetric results3 had shown that the reaction peak moved to higher temperatures and the temperature range was reduced with increasing water vapor pressure. These results suggested that judicious selection of water vapor pressure in the retort could postpone dehydroxylation of one, or both, clays until the combustor. For an ash recycle process, decreased heat requirements in the retort would enable a reduction in the recycle ratio of hot combusted shale to the retort. Other studies68 have suggested that recycled, fully combusted, Australian Tertiary oil shale can cause oil coking in the retort; thus any reduction in the recycle ratio could also increase oil yields. The influence of water vapor pressure on the dehydroxylation of Nagoorin kaolinite and the dehydration and dehydroxylation of Rundle smectite concentrates has been examined in this work. The rehydration and rehydroxylation of the clays was also studied.
Experimental Section A kaolinite (C0.2 pm) concentrate was separated' from a Nagoorin oil shale sample. Although it contained some smectite, this concentrate was suitable for studying the effect of water vapor pressure on dehydroxylation because the mass loss arising from smectite dehydroxylation is small compared to the mass loss from the kaolinite. A sample of Georgia kaolinite was used for comparison. Smectite (x0.2Mm) was separated' from a sample from the Ramsay Crossing member of the Rundle deposit. This contained only trace amounts of kaolinite. For comparison, a sample of montmorillonite from Clay Spur, Wyoming, was used. The clays were equilibrated a t a relative humidity of 55% prior to analysis. A modified Cahn RG thermobalance, described previously: was used to obtain thermogravimetric (TG) data. Derivative thermogravimetric (DTG) curves were obtained from the TG data by applying a recursive digital filter in a smoothing routine.'O Powdered clay samples of about 10 mg were spread thinly on the (4) Brindley, G. W.; Sharp, J. H.; Patterson, J. H.; Narahari-achar, B. N. Am. Miner. 1967,52, 201. ( 5 ) Yeskis, D.; Koster van Groos, A. F.; Guggenheim, S.Am. Miner. 1985, 70, 159. (6) Levy, J. H. In 'Processing Characteristics of Australian Oil Shales; final report NERDD Project 702; Gannon, A. J., Wall, G. C., Eds.; Australian Department of Resources and Energy: Canberra, March 1986; 42-55. . - - - , -Annexes __ ._. . . .. - 2 - and- 1- 1- . (7) Levy, J. H.; Mallon, R. G., Wall, G. C. Fuel 1987, 66, 358. (8) Dung, N. V.; Wall, G. C.; Kastl, G. Fuel 1987, 66, 372. (9) Levy, J. H.; Whiite, T. J. Fuel 1988, 67., 1326. (10) Whittem, R. N.; Stliart, W. I.; L e vr, J. H. Thermochim. Acta 1982, 57, 235.
(11) Patterson, J. H. CSZRO Diu. Energy Chem. Rep. 1986, ECIIR017. (12) Hurst, V. J.; Kunkle, A. C. Clays Clay Miner. 1985, 33, 1.
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