red world of
edited by
W. C. FERNELIUS
State University Kent. OH 44242 HAROLD WITTCOFF Koor Chemicals Ltd. Beer-Sheva. Israel Kent
P.O.B. 60
Oil Shale-Heir
to the Petroleum Kingdom?
Y. Schachter' Bar-llan University, Ramat-Gan Israel Late in 1973, the industrialized West suddenly became aware of its vulnerable position because of its dependence on a repular, cheap, and plentiful supply petroleum. What has .. . of . happened since, wascertn~nlyfor;ieeath: here is a vital mater~ala h ~ u t t be exhausted in a few decades and nmcentrated in a few countries, most of which use only a small fraction of it. Such a situation naturally invited those who had it, to make the most of it and quickly, a t the expense of those who needed it. The predominance of petroleum as a source of energy and chemical raw materials has been of rather short duration. I t was preceded by coal; in the search for a petroleum substitute, coal is regarded as the number one candidate. Reserves are plentiful and deposits are more evenly spread over the globe. But is there no alternative? 011 Shale Of the different forms of fossil organic matter, oil shale is the least known and is almost unused. This is surprising considerine- how abundant it is. Accordine to some. it exceeds coal-and, morpovtr, the possibility uf extracting oil from it has been known for almost 300 vears ( I ). Possihlv. .. if we knew more about oil shale, we woulduse more of it. What Is 011 Shale? Oil shale is a rock (not necessarily shale) containing finely divided organic matter called kerogen. Kerogen is rather poorly defined as a fossil organic material insoluble in organic solvents. The kerogen content of different shales varies over wide limits. The largest deposits-which are in the United States and Brazil-contain on the average 12-16% kerogen. These may be taken as representative figures. Some effort has been made to elucidate the structure of kerogen. These studies are complicated by the fact that keroeen is liable to undereo chanees when i t is isolated from the " matrix; moreover, it cannot he converted into liquid form. Recent studies performed by different techniques ( 2 4 )have, however, given fairly consistent results. According to these, kerogen is a structured material. The main building blocks are polycyclic clusters with a low degree of unsaturation and aromatization in the ring structures. These units are held
together by bridges formed by methylene groups and heteroatoms (mainly sulfur and oxygen). The whole forms three-dimensional oolvmen. Its structure. hieh .. hvdroeen . .. content, and high a m o h t of volatile matter distinguish keroeen from wal. which would fall into the same definition of b h g insoluble. The chemical composition varies widely in kerogens from different sources. Table 1 gives some representative figures. The hydrogen tocarbon ratio is important. In the Weatern US shales (Green River), the atomic ratio is-1.5. A similar figure is found in many other shales. The main minerals in which the kerogen is embedded are calcite, dolomite, clay, and quartz. On beating, kerogen starts to decompose a t about 200°C. Commercial retorting temperatures are much higher-mostly around 500°C. Gaseous and liquid products are obtained, and "fixed carbon" or "char" remains on the mineral residue. The liquid is called shale oil. T h e amount of char is as much as 40-50% of the kerogen with most shales. With Green River shale, an exceptionally low value of 20-25% is obtained. How Much Oil Shale Is There? It is very hard to give a definite answer to such a question with respect to any mineral resource. The extent of known reserves depends not only on the effort invested in exploration, but also on the economic and technological constellation. For example, petroleum wells, which were abandoned as uneconomical years ago, are now being considered for enhanced recovery. Similarly, the accessibility of off-shore reservoirs has extended considerably our concepts of available oil resources. As far as shale oil is concerned, the amounts of monev expended for exploration and development of technology are miniscule compared to those invested in most other natural resources. Nevertheless, it can he stated with confidence that oil shale reserves exceed those of petroleum a t least by two
Table 1. Representallve Flgures for the Elemental Composltlon of Kerwens (In Percent bv Welahll Carbon Hydrogen
' Author is deceased. Please address correspondence to feature
editor.
750
Journal of Chemical Education
su1tur
Nitrogen oxmen
orders of magnitude and are probably larger than those of coal. This would make kerogen the most abundant fossil organic What is even more imnortant is the fact that oil matter (6). widely distributed, so that many countries that shale is lack oil could alleviate or solve their enerev hv re".nroblem . sorting to oil shale (7). Potentlal Uses of 011 Shale Oil shale can replace petroleum in its three main uses: transportation fuel, fuel for power production, and raw materials for petrochemicals. Shale 011 Production The first commercial oil shale venture started in France in 1838. Since then, oil shale industries have been operating in a dozen countries on three continents. Most of them were liquidated during the fifties and sixties when one could buy a barrel of crude oil for $2.00 or less. At present, shale oil is produced in two countries: USSR (mainly Estonia) and China. Estonia possesses a particularly rich shale: -4W kerogen. The maior use is as a fuel for a 3200 MW Dower dant. Shale oil and vAous chemicals are minor produc& of the Russian oil shale industry. The Chinese industry uses a very poor shale (-3.5% oil). I t is viable because of the fact that the shale overlies a laree coal deoosit. The united States possesses the largest known reserves of oil shale and has never used them commercially. However, a major effort in the design of retorts has been in progress in this country since World War 11. Retorts can he divided into directly and indirectly heated. An example of the former is the gas comhustion or Paraho retort, in which the raw shale enters a t the top of a cylindrical furnace and moves down through the preheating, retorting, burning, and cooling zone. In the burning zones, part of the recycled product gas and fixed carhon are burned to supply the heat required for retorting. The Tosco retort is one of several indirectly-heated models. In this retort, the shale is contacted with ceramic halls that are heated in a separate vessel hy burning the product gases. The Brazilian Petrosix retort was designed by Cameron and Jones. who huilt the eas comhustion retort. and is. in essence. an indirectly heatedUparahoretort. I t is capable of heating 2000 tons of shale oer dav from which 1000 barrels of oil are produced. I t is thLlargesi retort ever built. Above-surface retorting requires the mining of vast amounts of rock and the disposal of considerable ash. It appears that these problems can he circumvented by retorting the shale in situ. A vast experimental program that has been in progress since 1965, mainly under US Government sponsorship, has so far met with little success. The operation is difficult-tocontrol and the yields are low. Also, environmental problems are not eliminated and, in particular, pollution of the sub-surface water tahle occurs. Sinre 1975, rffuru have been concentrated on the modified in situ process in which part of the shale is mined, leaving a subterranean chamber. Then part of the roof is blasted, filling the chamber with "rubbled" shale. This is ignited and retorted. The modified process bas bad more suceess than the true in situ one, but about 30% of the shale has to he discarded or retorted ahove
--Shale oil is a very heavy black liquid. Its hydrocarbon con-
tent is mainly aromatic and olefinic. Morever, i t contains sulfur and nitrogen. In order to convert it into feedstock that can he moved to petroleum refineries, it must first undergo a number of operations: coking (thermal cracking), elimination of sulfur and nitrogen (by catalytic treatment with hydrogen), and hydrogenation, Combustion In manv countries oil is consumed to a laree " extent for the production of power. In these cases, it is much more logical to burn oil shale as such. Shale had been burned in the nlant at Autun (France) (8) and the idea was picked up at the hegin-
Table 2. ComposMon of Gaswlcatlon Products at Differen( Temperatures in kg gas11000 kg shale 780'
withsteam
630'
780'
-
0.2
2.3
5.1
4.1 2.9 5.7 4.9 32.5
7.9 2.1 9.3 7.6 72.7
11.2
12.0
Nil
Nil
15.9 21.6 122.1
8.9 26.1 137.0
17.6
27.1
51.0
54.1
H2 CHI C2Hs C2H4
CO
c01 Total kggar/1000 kg shale(withoutC02)
870'
ning of the fifties in Israel 19-21 ), where almost half of the imported oil is burned in power stations. At present, oil shale is used as fuel for power production in Estonia, as mentioned previously. More significantly, although on a much smaller scale, is the operation at Dotternhausen (W. Germany). While the Estonian shale has a calorific value of 2200 kcallkg, the German shale yields only 700-900 kcallkg. The plant in Germany consumes 800 tons per day and produced 7 MW power. The shale ashes are used in the production of cement. The nlant has been in oneration since 1961 (12).
Combustion has manv advantaees in cornoarison with shale oil production, in particular, theiare (1) he energy content is almost fully exploited, whereas in most shales, almost half of the kerogen remains with the residue upon oil retorting; and (2) the investment and oneratine costs of the treatment of shale oil are saved. In spite of its high ash content, oil shale burns very easily. Recent pilot plant studies of fluidized bed comhustion have shown that as much as 2.5 X 106kcal can be obtained per hour per square meter (2). The softening point of the ash is generally well ahove the combustion temperature. Moreover, manv oilshales contain earth alkali carho"ates which are converted intouxides. These react verv readd\ with the SO, in the flue gases. In all these respects, bil shale is superior coal. Gaslflcatlon The Institute of Gas Technology (IGT) of Chicago has studied the hydrogasification of oil shale intermittently since the beginning of the 60's. Representative conditions are about 70 atm and 700°C (14). The author decided to avoid the use of hydrogen and pressure in his studies. The reasoning was that oil shale was such a poor material that investment and operating costs must be kept as low as possible. Kerogen can, in fact, be converted into gas by retorting a t atmospheric pressure a t higher temperature. The residual carhon can be reacted with steam. carbon dioxide. or air. The evolution of gases takes less than second; the rektion of the char takes a few tens of seconds (15). Table 2 lists the reaction products at different temperatures; the last column shows the nroducts obtained a t 780°C with steam. An analysis of the reaction sequence reveals that the following reactions have taken place on heating: 1) Cracking 2) Water gas reaction C +HzO-CotHz 3) Water gas shift reaction CO + Hz0 COa t Ha 4) Methanation CO+~HZ-CHI+HZ 5) Boudouart reaction C COI 2CO In addition, hydrogen sulfide formed by the decomposition of organic sulfur compounds reacts with earth alkali oxides so that the gases obtained at the higher temperatures are free from sulfur. It is certainly remarkable that these reactions should occur a t atmospheric pressure, relatively low temperatures, without the intervention of a catalyst, and at very fast sneed. This is a conseauence of the fact that the keroeen ~"~ is ext'remely finely subdiiided within the matrix so that it possesses a very high specific surface (surface per unit volume).
a
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Volume GO
Number 9
Se~tember1983
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751
What is Wrong With 011 Shale? The difficulty in the exploitation of oil shale lies in the fact that huge quantities of useless material must be handled and disposed of. Moreover, Green River shale contains soluble minerals which, when brought to the surface, would he leached out and would raise the salt content of the soil and the Colorado River. While these are admittedly very difficult environmental problems, it would seem that if a commensurate effort were made to arrive a t a solution and given a certain measure of reasonableness on the part of all involved, the use of this vast energy source could become possible. In particular, the overridine.. imoortance of the time factor should he . stressed.'l'ht~US spmdiimwthing likeSlSU.(KX)cveryminute for i r n ~ w t t doil. 'The aurstiom that must be nnked is hou long the economy can survive such an enormous bloodletting? Oil Shale or Coal The question cannot, of course, he put in this manner. The oosition of coal in the enerw picture of the near future is well secured. But there shouldbea place for oil shale. Kerogen is much easier to burn and to convert into liquids and gases than coal because of the high reactivity and relatively high hydrogen content of kerogen. It is not an exaggeration to state that it approaches in its behavior, petroleum, even though it is a solid. The exploitation of oil shale would lessen capital investment in energy, ease the burden on the industry of producing chemical equipment, and-most important of allshorten lead times.
752
Journal of Chemical Education
The Lesson We started by pointing out that the petroleum crisis could have been foreseen-and, in fact, it was foreseen by some whose voices were ignored. Now, let us ask ourselves: could something similar happen with other materials in the future? Not necessarily through cartellization as with petroleum, or through cutting off of supply as has repeatedly happened in war time. hut in a more natural way throuah exhaustion of reserves. In courses in applied chemistry, material science, and others, we often discuss the use of materials. It would be not just an intellectual exercise to devote some thought to the question of replacing them. Literature Clted (11 &la, M.at d.B. P.R3(1. 1694. 121 schmidt~co~urus, J. ~ . , ~P" P d ~ ~n.,~CCs~iiiiiid ,C. T ~ C ~ D O I O~ ~ Yr oSi~~ ~I~?ADD Arhor Science Puhlishors I n c . Ann Arbor. MI. 1975. p. 183. (31 Yen, T. F., "Science and Technolwy of Oil Shale.)' p. 193. 141 F.gel-Thal. M.. Datorsl Theais. Bar-llan University. Ramat-Can, Israel. 1975. I51 J. Cham. Edue.Steff,l.C~~~. E~oc..55,2631197R1,56. I88 (1979). (6) C h e m En#.NPUXJune 13. 1977.p. 20. 17) "Utililstion of Oil Shele. Progress and Prospee~1." United Nstiom. Department of EFonomicsndSuclal Affain, New York. 1967. (8) Labowl. H.. " P r a 9nd Oil Shale Cannel C d C n n f 1950?ht. ofPeMeum. London. 1951.p. 713. I91 Schbhter. 0.. B-ui. E.. Clark. E. I. ..and Gottesmann, E.. "Pm.Fourth World Petr. Con& 1955." Section IIIrn. No.4. Culomb. Rome. 1955,~. 457. (101 Lo"l,G..schachte.,O.,Basevi,E..Clark. E.L.,andGotksmann.E.."XllhSRfional Meetin& World Power Conference? &'om R.2. Pamr 17. -ad. 1957, p. 1.
( I l l Schkhter,Y., CHEMTECH,9,568.1979. (12) Frie8e.C.. Erndori undKohle. 14.702.1961. (13) Yauuskurt, S.. Gutfinger, C.,end Deysn. .I. Engine~rinrFoundstion FluidilationIII conc.. Hennilre,. N. H.. August 19RO. (14) Wsil. S.A..efal..Ado. C h m Ssr,No. 151.ACS. Wa8hington.D.C..p. 55. 1151 Sehschkr.Y.,Irr J olTechnolW.gy, 17.51, 1979.
