Energy & Fuels 1987, I , 248-252
248
Disruption of Kerogen-Mineral Interactions in Oil Shales M. Siskin,* G. Brons, and J. F. Payack, Jr. Corporate Research Laboratories, Exxon Research & Engineering Company, Annandale, New Jersey 08801 Received October 24, 1986. Revised Manuscript Received December 29, 1986
The interactions of representative organic model compounds with the major minerals present in oil shales were studied by using TGA desorption and FTIR methods. The results identified acid-base interactions between organics and clays as the principal chemical interaction responsible for binding the kerogen to the rock. On the basis of this conclusion, mildly acidic ammonium salt solutions were used to simultaneously create porosity, disrupt these interactions, and produce an enriched kerogen from Green River oil shale. The aqueous ammonium sulfate (pH -5-6) decomposes the carbonate minerals in the shale, which then allows the ammonia molecule and the ammonium ion to reach the kerogen-clay binding sites and disrupt the organic-clay interactions. With the use of aqueous ammonium sulfate at 85 OC, a 3-fold enrichment of organics was achieved by removal of 85% of the shale minerals with >95% recovery of the total shale kerogen.
Wettability methods are based on the principles of differential wetting of the kerogen and the minerals by two Three main approaches have been taken by previous immiscible liquids such as a hydrocarbon and water. The workers to separate organic kerogen from inorganic minkerogen is wet by the organic liquid phase and the minerals erals in oil shales and to recover an unaltered kerogen for are wet by the water phase, resulting in the kerogen being characterization studies: (1)differential wettability;l-' (2) retained in the hydrocarbon phase and the minerals being sink-float separations;s-12 (3) chemical method~.~l-~O released into the water phase. Periodic changing of the water phase results in mineral reduction. New surfaces on the hydrocarbon-kerogen phase are created by a mixing (1) Quass, F. W. J. Inst. P e t . 1939, 25, 813. or grinding action (e.g. in ball milling). This method has (2) Himus, G. W.; Basak, G. C. Fuel 1949,28,57-65. met with limited success and usually requires grinding the (3) Dancy, T. E.; Giedroyc, V. J. Inst. Pet. 1950,36,593-603,607-623. shale into fine (85% of the organics were removed in a majority of the cases (Table V). The reactive diene systems of benzofuran and to a lesser extent the indoles have probably undergone some acid-catalyzed polymerizations in the clay. The interactions with illite proved to be more difficult to disrupt with ammonium sulfate, with several model systems retaining between 10 and 67 wt % of the organics (Table VI). There does not appear to be any obvious trend in removal difficulty by compound type, basicity, or polarity to indicate which compounds were the most difficult to remove from the illite. Disruption of Kerogen-Mineral Interactions in Green River Oil Shale. Reagents capable of disrupting organic-clay, donor-acceptor interactions with model
rated, were pyrolyzed for 10 min at 500 OC (Tables I11 and IV). Since they were not bonded to the continuous organic network as present in the shale, large amounts (92-100%) of the model compounds were liberated during the pyrolysis, except in three cases. The pyrrolic and amphoteric N-model compounds and unsubstituted ammonium ion were the mwt difficult to remove from Ca-montmorillonite by pyrolysis. About 15-40 wt % of these materials were retained by the calcium-montmorillonite. Virtually all the model compounds were quantitatively removed from illite. From FTIR and elemental analyses of the pyrolysis residues, it is clear that several of the model compounds underwent reactions presumably catalyzed by the acidic properties of the clay under these conditions. These include the formation of ammonium ion by acid-catalyzed hydrolysis of the amides and the aromatic nitrile. These results imply that if the organics were not chemically cross-linked in oil shales, much larger quantities of nitrogen
Table VII. Mineral Distributions from Ammonium Sulfate Enrichment of Green River Oil Shale w i t h Toluene at 85 O C for 72 h (pHI5.3; pHF 8.0) % minerals % of whole % shale carbonates quartz albite pyrite illite organics 2.0 10.9 21.8 40.6 16.7 7.6 whole shale (21.8 wt % organic) kerogen fraction (62.2 w t % organic) 33.1 3.0 3.1 1.2 1.4 3.0 21.4 aqueous (dissolved) 37.6 37.6 0 0 0 0 0 mineral fraction 28.9 0 13.6 6.4 0.6 7.9 0.4 % removed from whole shale
92.6
81.4
84.2
30.0
72.5
1.8
252 Energy & Fuels, Vol. 1, No. 3, 1987
Siskin et al.
compounds were extended to Green River oil shale. Green River oil shale (21.8 wt % organic, C1a143.6N3,5,5180-100 mesh) was contacted with 2 M aqueous ammonium sulfate for 72 h at 85 OC. Ammonium carbonate formed during the decomposition of calcite and dolomite was deposited on the water-cooled condenser walls. As interactions were disrupted, the kerogen (density 1g/mL) floated, while the minerals (density >2 g/mL) sank. A water-insoluble organic solvent (e.g. toluene) served to wet and swell (50 vol % ) the liberated kerogen and kept it physically separated from the aqueous solution and separated minerals. The kerogen was removed from the top of the vessel. It was a dark brown material containing 62 wt % organics and containing 98% of the original kerogen in the shale (Table VII). The enriched fraction contained -38 wt % minerals (15% of the original shale minerals, which are mostly quartz and sodium feldspar (albite)). About 73 wt % of the original clay mineral, illite, was removed. The sink, or mineral fraction, was a white mixture of quartz, albite, and illite and contained less than 2 wt % of the kerogen from the starting shale. Over 90% of the carbonate minerals in the starting shale were decomposed. The enriched product, C100H144.7N3.6, appears to be unaltered by the mild treatment and can be used for chemical characterization studies.
-
Experimental Section Pyrolysis of Model Compound-Mineral Systems. Each model compound-clay system (1.0 g) was placed in a quartz tube assembly through which nitrogen was continuously purged (40 cm3/min) and placed in a minipyrolyzer at 500 "C for 10 min. T h e apparatus and procedure has been previously described in detaiLs2 T h e residue was analyzed for percent carbon and/or nitrogen to determine the amount of organics removed from the clay. ~~
~~
~
~~
(51)Corrected for hydrogen in dawsonite (NaA1(OH)2C03 (0.04 wt %)), analcime (NaAlSi2O6.H20 (0.03 wt %)), and illite (KO7Al2(Si3Al)0,0(OH)2(0.09 wt %)). (52) Siskin, M.; Aczel, T. Fuel 1983, 62, 1321-6.
Reaction of Model Systems w i t h Ammonium S u l f a t e for 72 h at 100 "C. To each model compound-clay (0.5 g) system was added 1M ammonium sulfate solution (50 mL). The reaction mixture was stirred and heated to reflux under nitrogen for 72 h. After this, it was cooled to room temperature and filtered. The solid product was dried in a vacuum oven for 16 h at 110 "C and analyzed for percent carbon and/or nitrogen to determine the amount of each compound removed from the clay. P r o c e d u r e f o r Ammonium Sulfate/Solvent E n r i c h m e n t of Green River Oil Shale. Green River oil shale containing 21.8 wt % organic matter (5.00 g, or 1.09 g of kerogen, -80/100 mesh) was charged into a 250-mL round-bottom flask with a magnetic stir bar. Ammonium sulfate (50 mL, 2.0 M) was then added, followed by the toluene (30 mL). The vessel, with attached cooling condenser, was kept under nitrogen throughout. The mixture was stirred and refluxed at 85 "C for 12 h. T h e heat was then removed and the stirring stopped. After the phases were allowed to separate (2-3 min), the aqueous/mineral layer was solidified by freezing the lower portion of the vessel in liquid nitrogen. The toluene/kerogen layer was then poured into a Buchner funnel lined with filter paper made of Teflon resin, diluted with methanol, and filtered. After the aqueous/mineral layer was allowed to return to room temperature, this mixture was also filtered through a second Buchner funnel. Both cuts were washed with water (8 X 500 mL) and methanol (4 X 500 mL). The products were dried in a vacuum oven at 100 "C overnight to yield 1.63 g of a brown kerogen fraction and 1.55 g of a white mineral fraction.
Acknowledgment. The authors wish to thank Drs. D. Pevear, M. L. Gorbaty, and W. N. Olmstead for helpful discussions and Drs. R. I. Botto and N. Guven (Texas Tech University) for carrying out the XRD mineral identifications. Registry No. Heptylamine, 111-68-2; quinaldine, 91-63-4; pyridine, 110-86-1;2-hydroxypyridine, 72762-00-6; 1-methylindole, 603-76-9; 1,2-dimethylindole, 875-79-6; acetamide, 60-35-5; benzamide, 55-21-0; 2-octanone, 111-13-7; methyl laurate, 111-82-0; phenyl ether, 101-84-8; benzofuran, 271-89-6; pyrene, 129-00-0; 1-phenyloctane, 2189-60-8; 1-nonene, 124-11-8; indole, 120-72-9; lauric acid, 143-07-7;calcium-montmorillonite, 1318-93-0; illite, 12173-60-3;benzonitrile, 100-47-0; ammonium sulfate, 7783-20-2; dolomite, 16389-88-1;calcite, 13397-26-7;quartz, 14808-60-7;albite, 12244-10-9; pyrite, 1309-36-0.
