Energy & Fuels 1989, 3, 109-111
109
Table 11. Mineral Distributions' from Ammonium Sulfate Enrichment of Rundle Ramsay Crossing Oil Shale with Rundle Ramsay Crossing Shale Oil in Xylenes at 90 'C for 21 h % of % minerals whole % shale quartz plagioclasea illite smectiteo kaolinite' pyrite carbonates organics whole shale (19.1 wt % organic) 100.0 23.2 10.7 11.4 21.7 2.4 1.1 8.5 19.1 kerogen fraction (32.3 wt % organic) 46.1 6.3 3.0 5.2 10.1 3.8 0.7 0.7 14.2 aqueous (dissolved) 11.8 7.8 mineral fraction 42.1 12.9 3.2 5.9 8.5 3.0 0.5 6.1 % removed from whole shale
72.8
72.0
54.4
53.5
a
36.4
91.8
25.7
Plagioclase and smectite under aqueous hydrolysis conditions form some kaolinite, silica gel, and hydroxides.'
allows the ammonia molecule and the ammonium ion to reach the kerogen-clay binding sites and disrupt the organic-clay interactions. Toluene was used as a water-insoluble organic solvent in the system to wet and swell the liberated kerogen and keep it physically separated from the aqueous solution and separated insoluble minerals. Removal of 83% of the minerals with >95% recovery of the kerogen achieved a 3-fold enrichment on Green River oil shale. We now find that the ability of the water-insoluble organic solvent to wet and swell the kerogen and to match ita solubility parameter can be crucial to effecting the enrichment procedure. The same enrichment approach used for Green River oil shale was not successful on Rundle shales. The major clay minerals in Rundle shales are smectites vs the illite in Green River oil shale, and the carbonate mineral content of the Rundle shales is much lower (-9% vs -40%). However, even with these compositional differences there was no a priori reason to alter our previous conclusions that ammonia and ammonium ions should still be the reagents of choice for disrupting kerogen-mineral interactions. The fact that this procedure was effective in disrupting interactions of model organics with the smectite, calciummontmorillonite, further reinforced our conclusion.' However, careful examination of the beneficiation reaction in progress indicated that the inability of the toluene to wet the Rundle kerogen and increase its hydrophobicity could be the bottleneck to effecting the disruption of interactions and to having the enriched kerogen produced associate with the water-insoluble hydrocarbon layer in the system. Because the Rundle kerogen (ClooH161N1,85So.709.2) is much richer in oxygen than Green River kerogen (Cl&144N3,6So.700.5) and contains a higher concentration of C20-C30aliphatic carbon chains throughout the structure: we tried, unsuccessfully, to overcome the wettability problem by substituting 2-heptanol and/or hexadecane for the toluene employed in the Green River system. A series of swelling studies was then carried out to identify solvent systems that would wet the kerogen most effectively and keep enriched, separated, kerogen isolated from the aqueous system (Table I). Methanol and pyridine are the best swelling solvents for the oil shale, but they are also water soluble. A xylene containing Rundle or Green River shale oil, generated by retorting, swells the raw shale a reasonable amount (15%) and is not water soluble. Because the oils are generated from actual shales, the ring types and distribution of heterocyclic nitrogen should provide a close solubility parameter match to those in the kerogen. After prewetting the shale with the Rundle oil (10% in xylenes) for 15 min at 90 "C, we observed that the whole shale remained in the organic layer for the first time. The beneficiation (2) Scouten, C. G.; Siskin, M.; Aczel, T.; Rose, K. D.; Colgrove, S. G.; Pabst, R. E., Jr. Proceedings of the 4th Australian Workshop on Oil Shale; ANSTO Lucas Heights, NSW, Australia, 1987; p 94.
procedure was then carried out by using the Rundle Ramsay Crossing oil shale (RXOS) (5.0 g, 80-100 mesh), ammonium sulfate (50 mL, 2M), and a mixture of Rundle Ramsay Crossing shale oil (10.6%)in xylenes (50 mL) for 21 h at 90 OC. The organic layer was removed from the top of the vessel and fiitered to recover a dark brown solid. This enriched kerogen contained 32 w t % organic material, which represents almost a 2-fold enrichment. About 75% recovery of the kerogen (Table 11)was achieved, and over 50% of the original clay minerals and 70% of the quartz and feldspars were precipitated while 90% of the carbonates were dissolved. The results indicate that our approach to overcoming the wetting problem to produce an enriched and structurally unaltered kerogen was directionally correct. Acknowledgment. We thank Dr. David Pevear for very helpful discussions during the course of this work. Registry No. Hexadecane, 544-76-3; pentane, 109-66-0; toluene, 108-88-3; 2-heptanol,543-49-7; tetrahydrofuran, 109-99-9; carbon tetrachloride,56-23-5; xylene, 1330-20-7; pyridine, 110-86-1; methanol, 67-56-1; quartz, 14808-60-7;illite, 12173-60-3;kaolinite, 1318-74-7; pyrite, 1309-36-0; ammonium sulfate, 7783-20-2. (3! Brons, G.;Siskin, M.; Botto, R. I.; Guven, N. Energy Fuels, paper in this issue. (4) Murphy, W. M.; Helgeson,H. C. Geochim. Cosmochim. Acta 1987, 51, 3137.
M. Siskin,* G. Brons, J. F. Payack, Jr. Corporate Research Laboratories Exxon Research and Engineering Co. Annandale, New Jersey 08801 Received June 27, 1988 Revised Manuscript Received September 7, 1988
Contribution of Normal Paraffins to the Octane Pool
Sir: Normal paraffins are among the lowest octane compounds in gasoline, and the octane number of a gasoline can be increased by their elimination. In this work, the contributions of the C5-Cgnormal paraffins to the octane number of petroleum reformates and naphthas is determined. It is shown that in most cases these paraffins exhibit higher blending octane numbers with reformates and naphthas than would be expected from their pure compound octane numbers, and that these blending numbers increase as the octane number of the base fuel into which they are blended increases. The current drive to reduce and eventually eliminate lead additives from gasoline is forcing petroleum refiners to look for new ways to meet the projected octane demand. Many of the options for increasing the octane pool involve processes that decrease the concentration of the lowest octane components of the gasoline pool. 0 1989 American Chemical Society
Communications
110 Energy &Fuels, Vol. 3, No. 1, 1989 Table I. Research Octane Number (RON) of Normal Paraffin Blends RON of 10 vol % blend of normal paraffin in base stock base stock Dentane hexane heDtane octane nonane ce-143 OC
65.3
62.6
60.1
57.8
55.2
CB-143 OC
petroleum naphtha, 66.2 RON ce-180 "C
77.2
74.1
72.2
70.9
68.8
96.1
91.6
91.0
89.7
89.7
petroleum reformate, 97.0 RON
It is well-known that octane number varies with the boiling range and chemical composition of the hydrocarbons present in a gasoline and that normal paraffins are generally the lowest octane component in a given boiling range. Therefore, many octane upgrading schemes are aimed at decreasing the concentration of normal paraffins in the gasoline pool. This is accomplished either by selective sorption and removal of normal paraffins or by their catalytic conversion to higher octane hydrocarbons.' In evaluating the benefits of schemes aimed at removal or conversion of normal paraffins, it is useful to be able to estimate the potential octane boost. The octane number of any fuel is defined as the percent isooctane (2,2,4-trimethylpentane) required in a reference blend of normal heptane and isooctane to give the same engine knock performance as that fuel. The RON (research octane number) of normal heptane and isooctane are arbitrarily defined as zero and 100 respectively, and these two paraffins blend linearly by definition. However, the RON of a blend of any other pure compounds or refiiery streams is not necessarily the linearly weighted sum of the RON of the individual components. It is well-known, and has been often demonstrated, that octanes do not blend linea r l ~ . ~ ~ ~ In this work, reagent grade normal pentane, hexane, heptane, octane, and nonane are blended with three different refinery-derived base fuels. The purity of all paraffins used in this study exceeded 99%, and they were used as received without prepreatment or further purification. Each blend contained 10 vol % of the normal paraffin being studied and 90 vol % of one of the base fuels. The base fuels included a straight-run c6-145 "C naphtha and two different C6-180 OC reformates. The naphtha and one of the reformates had been catalytically processed in a pilot plant to selectively remove most (>80%) of their normal paraffin^.^ ASTM Method D2699 was used in determining the octane number for the three base fuels and the 15 blends in this study. One octane determination was made for each blend, while the reported base fuel RON is the average of three ASTM D-2699 determinations. In order to insure consistency in the octane determinations, the octane number of each base fuel and all blends with that base fuel were performed by (1) Weiszmann, J. A.; Dauria, J. H.; McWilliams, F. G.; Hibbs, F. M. Hydrocarbon Process. 1986, 65(6), 41. (2) Knocking Characteristics of Pure Hydrocarbons; ASTM Special Technical Publication No. 225; ASTM: Philadelphia, PA, 1958. ( 3 ) Rusin, M. R.; Chung, H. S.; Marshall,J. F. Ind. Eng. Chem. Fundam. 1981,20, 195. (4) Burd, S. D.; Maziuk, J. Hydrocarbon Process. 1972, 51(5), 97.
57.2
30.2
5.2
-17.8
-43.8
59.2
28.2
9.2
-3.8
-24.8
88.0
43.0
37.0
24.0
24.0
petroleum naphtha, 66.2 RON ce-180 o c
petroleum reformate, 79.2 RON Ce-180 OC
Table 11. Calculated Blending Research Octane Number (RON) of Normal Paraffins blending RON of normal paraffins based on RON of blends in Table I base stock pentane hexane heptane octane nonane pure paraffin2 61.7 24.8 0.0
petroleum reformate, 79.2 RON Ce-180 "C
petroleum reformate, 97.0 RON
i .HEXANE HEPTANE
0 -A
-
0
v
-50 65
'
I
1
I
I
I
70
75
80
85
90
95
100
OCTANE NUMBER OF BASE STOCK (RON)
Figure 1. Blending octane number of normal paraffins in petroleum base stocks.
a single operator in the same test engine on the same day. Table I gives the measured RON of all blends in this study. It can be seen that the octane number of the blend generally decreases as the carbon number of the normal paraffin in the 10% blend increased. The one exception to this trend is with the 97.0 RON reformate, where the 10% blends with normal octane and nonane gave equivalent knock performance. The calculated linear volumetric blending RON for each of the normal paraffins in each of the reference fuels in this study is given in Table 11. A plot of these data in Figure 1shows that the blending numbers of the normal paraffins in this study varied with the RON of the base fuel into which they were blended. The blending numbers when blended into the 97.0 RON reference fuel were 13-68 numbers higher than when blended into the 66.2 RON reference fuel. The variation in blending octane number with base fuel octane number shown in Figure 1may not apply for these normal paraffins in all base stocks. But in the absence of other data, it can be used as a first approximation for estimating the blending octane numbers of these normal paraffins. Octane number is a measure of a fuel's resistance to autoignition on compression. Apparently when normal paraffins are compressed in the presence of a mixture of higher octane hydrocarbons, their tendency to autoignite is reduced more than would be expected on the basis of a volumetrically weighted average of the octane numbers of the pure paraffin and the base stock. It is important to recognize this nonlinearity when estimating the octane upgrading potential of any process aimed at removing normal paraffins from the octane pool.
Book Reviews The data presented here demonstrate that at the 10 vol % level, normal paraffins blend synere;istidy with tmical - -
petroleum basestocks in most cases. This-synergism is small and probably not statistically significant when the lower octane base stocks were blended with the higher octane paraffins (i.e. pentane and hexane in the 66.2 RON and 79.2 RON base stocks). However, this svneraism is significant when any of the normal paraffins &e biended with a more typical high-octane stream.
Energy &Fuels, Vol. 3, No. 1, 1989 111
Registry No. Pentane, 109-66-0;hexane, 110-54-3;heptane, 142-82-5; octane, 111-65-9; nonane, 111-84-2.
R. H. Heck Mobil Research and Development Corporation Central Research Laboratory, P.O.Box 1025 Princeton, New Jersey 08540 Received April 25, 1988 Revised Manuscript Received November 2, 1988
Book Reviews NMR of Humic Substances a n d Coal. Edited by R. L. Wershaw and M. A. Mikita. Lewis Publishers, Inc.: Chelsea, MI. 1987. 236 pp. $49.95.
This book, a collection of papers presented at the Eighth Rocky Mountain Regional Meeting of the America1 Chemical Society (ACS), might have been more appropriately published in the ACS Symposium Series. The title proposes a comprehensive treatise; however, because the book is a disjointed collection of chapters dealing mostly with humic substances, it fails to be complete in its treatment of the subject. Chapter 1, by R. L. Wershaw and M. A. Mikita, sets a negative tone for the book by discussing why an evaluation of NMR techniques is necessary and by highlighting the fact that the reader must be aware of the many pitfalls of NMR spectroscopy. Chapter 2, a marvelous review by C. M. Preston, concerns the application of solution NMR methods to the study of humic substances and discusses the relation of solution NMR to solid-state NMR techniques. Chapter 3, by G. E. Maciel and his associates, is a review of the solid-state 13CNMR of humic substances and includes the introduction of a new solid-state ‘H N M R method (CRAMPS) that shows some promise in structural characterization. Chapter 4 is a review of ESR spectroscopy by C. Stellink that seems to be a bit misplaced in this book but does nontheless partially bridge the gap between ESR and NMR. Chapter 5 is a review by M. Mikita of various derivatization methods used to incorporate NMR sensitive nuclei into humic substances and coal, thereby allowing for additional structural information. Chapter 6 is an excellent paper by L. W. Dennis and R. E. Pabst that describes some 2-D solution NMR studies of humic substances and fossil fuel liquids. These 2-D experiments likely will provide a substantial amount of new information about the nature of structural components. Chapter 7 is a brief discussion by E. Fukushima of wide-line NMR techniques. Chapter 8 by D. E. Axelson describes a means of detecting the mobile components in coal by some second-generation solid-state I3C NMR methods. This chapter is a bit premature in its discussion of the subject matter because it deals with a complex and controversial issue in coal science and little has been said to this point in the book about NMR of coal; in fact, little is said about coal throughout the book. Chapter 9 by W. L. Earl is another chapter that emphasizes many of the drawbacks of solid-state I3C NMR without reinforcing the advantages. Earl suggests that the Armadale fulvic acid must be cooled to -56 OC to obtain a spectrum that he considers representative of the carbon distributions; however, the spectrum is identical with other published spectra of the same material taken at room temperature. Chapter 10 by R. L. Wershaw and D. J. Pinckney is a reiteration of previous papers by Wershaw that proposed a membrane model for soil humic acids. Their inclusion of NMR evidence for a “mobile” component, which is discussed in Chapter 9, does little to support the model, especially because the mobility arguments discussed by Earl are problematic. Chapter 11 by A. M. Vassallo is a noteworthy review of factors affecting signal intensities in
solid-state 13C NMR of humic substances. The negative tone of the fiial chapter, Chapter 12, an overview by the editors, contrasts sharply with the positive views of NMR potential-views that are shared by so many experts in this field, including some of this book‘s contributors. I concur with Mikita and Wershaw that we must be aware of the disadvantages of any analytical technique; however, the editors have disproportionately stressed the pitfalls of NMR. NMR is a promising and important new tool for the structural characterization of complex substances, such as humic substances and coal. I hesitate to recommend this book for anyone attempting to learn more about the advantages of applying NMR methods to the study of humic substances and coal. For those already familiar with NMR applications, I urge them to read some of the better chapters but not to allow the pessimistic tone to unduly influence them. Patrick G. Hatcher, U.S. Geological Survey
Coal-The Energy Source of the Past and Future. By Harold H. Schobert. American Chemical Society: Washington, DC. 1987. 282 pp + index. Clothbound: US and Canada, $29.95; export, $35.95. Paperbound: US and Canada, $19.95; export, $23.95. This book covers an immense range of information, including chapters on the origin of coal, the world distribution of coal, the chemistry and physics of coal, coal mining, transportation, production of electric power and heat, coking and ore reduction, and chemicals from coal and two chapters on coal-based fluid fuels. Footnotes and an Appendix suggest further reading from a variety of sources, ranging from the World Book Encyclopedia to the Lowry-Elliott volumes on The Chemistry of Coal Utilization. A good index is provided. The author, a professor of fuel science a t The Pennsylvania State University, has an extensive background in fossil fuels and is obviously widely read. He has written a highly literate and balanced monograph covering virtually every aspect of coal, including historical, social, and environmental dimensions. Most of us engaged in fossil energy research feel that we “know” coal. However, even those with many years’ experience with coal will find this small book well worth reading. Did you know that the soot deposition in Pittsburgh in the year 1911 was approximately lo00 tons per square mile? Or that coal combustion is currently responsible for about one-fourth of the SO, released to the atmosphere? This book is packed with information that I feel better for knowing. Schobert writes with quiet and unobtrusive clarity, capturing the essentials from ancient mining practices to magnetohydrodynamics. His sense of the interplay of technological, economic, and political factors during and after the Industrial Revolution is impressive. Indeed, he places coal utilization in a cultural perspective to which scientists are seldom exposed. Throughout, his exposition is enlivened with bits of historical insight and etymological analysis. The original hope of the ACS editors was for a monograph
