438
Energy & Fuels 1987,1, 438-447
Investigation of the Chemical Basis of Kerosene (Jet Fuel) Specification Properties David J. Cookson, C. Paul Lloyd, and Brian E. Smith* Melbourne Research Laboratories, The Broken Hill Proprietary Co., Ltd., Mulgrave, Victoria 31 70, Australia Received June 16, 1987. Revised Manuscript Received August 10, 1987 Jet fuel properties, a number of which are routinely used to define fuel quality, have been investigated with a view to relating property values to fuel composition in a quantitative manner. Fuel composition is expressed in terms of the abundances of hydrocarbon compound classes (n-alkanes, branched plus cyclic saturates, monoaromatics, and diaromatics) and is determined by using HPLC and either GC or I3C NMR procedures. A suite of 78 fuels has been included in the study. These derive from petroleum sources (a range of disparate, mainly Australian, oils) and from upgraded synfuel sources (originating from coal hydroliquefaction, coke and char manufacture, oil shale pyrolysis, and peat pyrolysis). Properties considered include smoke point, vol % of aromatics, wt % of naphthalenes, 13CNMR aromaticity, ‘HNMR aromaticity, heat of combustion, elemental hydrogen content, freezing point, and specific gravity. It has been found that for each of these properties a simple linear function is effective in relating property values to compound class abundances. From these relationships it is possible to translate fuel quality specifications from constraints on fuel properties to constraints on chemical composition. This leads to the identification of a compositional domain that, within the limitations discussed herein, represents the target which must be achieved in any viable refining strategy. The possible use of jet fuel combustion quality specifications based on compound class composition or elemental hydrogen content is also discussed. Introduction The primary objective of this work has been to identify the target range of chemical compositions which must be achieved in order to yield hydrocarbon transport fuels that meet current fuel quality specifications. Kerosenes (190-230“C) for use as jet fuels are the focus of attention here. Diesel fuels will be discussed in a future publication. Fuel quality is not usually defined in chemically explicit terms. Thus a clear answer to the question of target chemical composition is not to be found in currently available literature, even though a number of broad expectations can be adduced.l-l In addition, transport fuel quality is not usually defined directly in terms of performance in a vehicle. Rather, the quality objectives of a refinery take the form of a series of secondary specifications that may be imposed by the customer, by the refinery, or by law. Such specifications are generally expressed in terms of fuel response to a set of standard laboratory test procedure^.^*^ For example, a Jet A fuel is usually required to show a smoke point of >20 mm, a heat of combustion of >42.8 MJ/kg, and a freezing point below -40 OC (see Table I). If reIevant fuel properties could be expressed as a function of composition, then fuel property specifications (such as those above) could be expressed as composition limits. Methods for determining fuel composition in terms of appropriate compound classes have been developed previousl*6 and have recently been extended and impr0ved.I HPLC results are combined with either 13CNMR or GC data to provide the weight fractions of n-alkanes, branched plus cyclic saturates, monoaromatics, and diaromatics. Our first attempts to relate such compositions to fuel property values were sufficiently successful6to lead to the current work. The number of properties considered has now been increased to 10 (see Table I) and the number of samples considered has been increased to a total of over 70 fuels, Author to whom correspondence should be addressed.
0887-0624/87/2501-0438$01.50/0
obtained from both petroleum sources and alternative (mainly coal synfuel) sources. Experimental Section Sample Origins. A total of 78 kerosene fuels, divided into three groups, have been used in this study. The fiit group (group A) consists of 42 kerosenes of which 39 were derived from the following geographically disparate Australian petroleum sources: Amadeus Basin (3); Bowen Basin (2);Browse Basin (1); Canning Basin (5); Carnarvon Basin (4); Cooper Basin (10); Eromanga Basin (6); Gippsland Basin (4); Perth Basin (2); Surat Basin (2). The three remaining kerosene fuels in this group are synfuels, which were produced by the direct hydroliquefaction of black coal (1)and brown coal (2) followed by hydrotreatment of the resultant synthetic crude oils. Of the second group of kerosenes (group B), 11 are derived from the following petroleum sources: Saudi Arabian “export” crude; Chinese (Daqing) “export“ crude; Gippsland/Minas (Indonesia) crude oil blend; Carnarvon Basin; Cooper Basin; Surat Basin; Amadeus/Carnarvon Basin blend; Amadeus/Cooper Basin blend; Gippsland/Cooper Basin blend. The remaining 12 group B samples are hydrotreated synfuels derived from coal syncrude (3), anthracene oil (61, pyrolyzed peat (2), and shale oil (1) feedstocks. The 13 samples in group C are all coal hydroliquefaction synfuels, derived from a single feedstock via different processing variants.s (1)Significance of Tests for Petroleum Products; Boldt, K., Hall, B. R., E&.; ASTM Special Technical Publication 7C, ASTM Philadelphia, 1981. (2) Criteria for Quality of Petroleum Products; Allinson, J. P., Ed., Applied Science Publishers: Barking, UK, 1973. (3) Annual Book of ASTM Standards, Section 5 , Petroleum Products, Lubrtcants and Fossil Fuels; American Society for Testing and Materials: Easton, MD, 1986. (4) IP Standards for Petroleum and its Products, Part I , Methods for Analysis and Testing; Wiley: Chichester, U.K., 1986. ( 5 ) Cookson, D. J.; Rix, C. J.; Shaw, I. M.; Smith, B. E. J. Chromatogr. 1984, 312, 237-246. (6) Cookson, D. J.; Latten, J. L.; Shaw, I. M.; Smith, B. E. Fuel 1985, 64, 509-519.
(7) Cookson, D. J.; Shaw, I. M.; Smith, B. E. Fuel 1987,66, 758-765. (8) Palmer, L. D.; Copson, V. B.; Danaher, W. J.; Johnston, P. A., Schulter, K. “Economic Feasibility of Producing Transport Fuels from Australian Coal”;end of grant report, NERDDP Project No. 642, Australian Commonwealth Department of Resources and Energy: 1986.
0 1987 American Chemical Society
Energy & F u e l s , Vol. 1, No. 5, 1987 439
Kerosene Properties
Table I. Listing of Jet Fuel Properties Investigated measmt method used IP57 ASTM D1319 ASTM D1840 13C NMR 'H NMR IP12 IP12 ASTM D3701 IP16 ASTM D4052
DroDertv smoke point aromatics content naphthalenes content carbon aromaticity hydrogen aromaticity gross heat of combustion net heat of combustion hydrogen content freezing point inverse specific gravity
units mm vol % wt%
atom % atom %
svmbol SP VaI Nap CaI
H.. Q,
Q"
"C cm3/g
Jet A spec (ASTM D1655) >20 mmn >20 vol % 42.8 MJ/kg, (D)specific gravity between 0.7750 and 0.8398 g/cm3, and (E)freezing point < -40 “C. The compositional requirements for a kerosene fuel to satisfy all of these specifications are shown in part F. This domain is simply obtained as the shaded area common to all of parts A-E. The borders of the specification domain, labeled a-d in part F, derive from (a) specific gravity, (b) smoke point, (c) aromatics content, and (d) freezing point. 13C NMR aromaticity (Figure 4A and ref 6), ‘H NMR aromaticity (Figure 4B; t6ough see ref 6 for .additional comments), hydrogen content (Figures 4C,D), specific gravity (Figure 4E; limited synfuel data) and heats of combustion (Figures 4F,G; limited synfuel data). No comment on freezing point is possible since none of the synfuels tested gave adequately defined freezing points. This is probably true of all fuels with compositions located in the lower left hand corner of Figure 1A (both synfuels and petroleum). Chemical View of Specification Properties. Property specifications for kerosene fuels are generally expressed in terms of a minimum or maximum requirement or as a range of acceptable values. We have expressed property values in terms of chemical composition and therefore can represent a specified property constraint as a composition constraint. In each ternary diagram in Figure 5 a set of fuel compositions compatible with a single property value (e.g. smoke point >20 mm) is represented by a single line with intercepts on the edges of the triangle that are readily determined from eq 1by using the coefficients in Tables I1 and 111. For a given property (e.g. smoke point), isoproperty lines are parallel. In Figure 5A fuels with smoke points >20 mm would have compositions to the left-hand side of the 20-mm line, whereas those with smoke points 20 mm), aromatics content (V, < 20 vol %), net heat of combustion (Q, > 42.8 MJ/kg), specific gravity (SG between 0.7750 and 0.8398 g/cm3), and freezing point (FP < -40 “C). The line of constraint labeled % H corresponds to a hydrogen content of 13.40wt. %. Fuels with compositions located to the left of this line will have % H > 13.40.
pecially attractive23in that those which meet the heat of combustion per unit mass requirement (Figure 5C)will have a relatively high heat of combustion per unit volume. This should give good aircraft r a n g e . l ~ ~It*is~ also ~ notable that the border labeled “c” in Figure 5F appears governed by a well-known but, nevertheless, indirect indicator of fuel performance, viz. volume percent of aromatics (see Figure 6). The border marked “d” in Figure 5F derives from the freezing point specification (see Figure 6) and is probably the least well-defined from the point of view of commercial jet fuels. Variation of boiling range is one of the major tools available to refiners in meeting stringent jet fuel specifications. For example, problems with a high freezing point might be overcome by lowering the initial boiling point of the cut. Other constraints (e.g. flash point) limit the extent to which this strategy may be pursued. As was discussed earlier, it is expected that the compositional dependence of freezing point will be considerably influenced by the boiling range of the fuel. Thus border “d” in Figure 5F must be regarded as specific to the boiling range studied here (190-230 “C). A lower initial boiling point would raise this border in Figure 5F. Alternatively, if the freezing point specification were changed from -40 to -50 “C, border “d” would move downward in Figure 5F. Alternative Specifications. Properties used to define jet fuel combustion quality have often been the subject of c r i t i ~ i s m . ~ It * ~is*notable ~ ~ $ ~ from ~ Figure 6 that, of the four combustion-related properties studied here, net heat of combustion (Qn)and smoke point (SP) are closely comparable in terms of their implied compositional constraints. The other two indicators, volume percent of aromatics (Vm) and specific gravity (SG), appear different. This suggests that fuels complying with some but not all of these specifications will exist and that in some cases (as discussed in the previous section) the controlling property may be a very indirect indicator of quality (e.g. SG or Vm). The question of whether such fuels actually would or would not perform adequately as jet fuels is beyond the scope of the current study. It is obvious from Figure 6 that fuel composition as defied herein could be used as an independent combustion quality specification if desired. This possibility (23) Franck, J. P.; LePage, J. F.; de Gaudemaris, G.; Bonnifay, P. ~ y d r o c ~ r b oProcess. n 1977, 287-289.
Cookson et al.
446 Energy & Fuels, Vol. 1, No. 5, 1987 Table VII. Linear Property Relationships for Group A Samples Involving Elemental Hydrogen Content Model 1: P = P ( % H) + h
P SP
var car
Har
no. of samples 24 26 27 27
Qll
21 21
FP SG-'
20 23
Q,
range of P 15-38 4.1-24.2 1.5-16.1 0.4-5.5 45.64-46.94 42.87-43.78 -50 to -32 1.1459-1.2863
R2 0.88 0.62 0.59 0.57 0.85 0.75 0.16 0.92
Model 2: % H = kP
P SP
var car
Har Qe
no. of samples 24 26 27 27 21
QIl
21
FP SG-I
20 23
range of % H 12.63-14.88 12.63-14.88 12.63-14.88 12.63-14.88 13.04-14.88 13.04-14.88 13.58-14.88 12.63-14.88
R2 0.88 0.62 0.59 0.57 0.85 0.75 0.16 0.92
rmse 2.1
3.5 2.6 0.9 0.16 0.15 4.1 0.01
P
h
10.63 -8.42 -6.10 -2.04 0.818 0.606 5.90 0.0652
-122.6 132.2 94.2 31.4 34.73 34.73 -123.9 0.326
k 0.084 -0.076 4.099 -0.289 1.045 1.261 0.035 14.16
m 11.82 15.14 14.94 14.89 -34.25 -40.44 15.65 -3.54
+m rmse 0.19 0.33 0.34 0.34 0.17 0.22 0.32 0.15
is not pursued in detail here, however, since it has not been the objective of this work to extend or alter current practices in defining fuel quality. For some time it has been suggested that elemental hydrogen content (% H)might be used as a fully adequate combustion quality s p e ~ i f i c a t i o n . ~ ~One , ~ ~way of addressing this question is to consider the relationships between existing specification properties and % H. Such relationships are shown in Figure 7 for SG-', Q,, V,, and SP. These and other relationships involving % H, in the form P = g(% H) + h (10) where g and h are constants, are listed in Table VII. A good linear relationship between SP and % H is apparent in Figure 7A. Indeed, the expression deemed best by Martel and Angello14 % H = 11.88 + O.O8254(SP) (11) is closely comparable to that found in the current work, viz. % H = 11.82 + 0.084(SP) (12) with R2 = 0.88 and rmse = 0.19%. Martel and Angello also estimated net heats of combustion for three specific hydrogen contents. These are shown as crosses in Figure 7C. Clearly these data are in close agreement with the linear correlation found in the present work (solid line in Figure 7C). Thus % H could be used to adequately define prerequisites for smoke point and net heat of combustion, since rmse values in Table VI1 (2.1 mm and 0.15 MJ/kg) are in gross accord with expected measurement errors. It is notable here that SP and Q, rmse values obtained from composition-property correlations (Tables I1 and 111)are closely comparable to those from % H correlations (Table VII). This implies that % H and compositional specifications appear similarly suitable. Figure 7D shows a reasonable linear relationship between SG-' and % H. The derived rmse (0.010 cm3/g), though marginally better than that obtained via property-composition relationships (0.013 cm3/g, Table 111), is (24) Vere, R. A. In Modern Petroleum Technology; Hobson, G. D., Ed., Wiley: Chichester, U.K., 1984; Part 2, Chapter 19.
35E .
25
75 12.0
13.0
-HYDROGEN
**
14.0
15r
CONTENT (wt%)-
Figure 7. Plots of the hydrogen content of kerosene fuels from versus group A (0 = petroleum, 0 = synfuel) and/or group C (0) (A) smoke point, (B) aromatics content, (C) net heat of combustion, and (D) inverse specific gravity. Except for aromatics content (B),the regression lines (full lines) relate to Model 1in Table VI1 and are calculated by using the relevant values of g and h. For aromatics content, the regression line (V, = -13.01 (% H) 198.2) is appropriate for petroleum-derived fuels only. The correlation between % H and V, for synfuel samples from groups A (0) and C (o), is indicated, qualitatively, by the dashed line in part B. For group C samples, V, data were calculated from eq 1 and the coefficients from Table 111. In part C the dashed line connects points (X) that correspond to the best estimates of Martell and A n g e l l ~for ' ~ net heat of combustion at three specific hydrogen contents. The vertical dashed line through parts A-D corresponds to a hydrogen content of 13.40 w t %.
+
still large in comparison with expected SG-' measurement errors. Thus if SG were a singularly important fuel specification, it would be unwise to use either % H or compound class composition as a secondary measure. SG of course, it only one of a number of indirect specifications and is not singularly preeminent. Unlike SP, Q,, and SG-l, V , does not correlate well with % H (Figure 7B). This is a simple consequence of the disparate % H contents of possible nonaromatic species as discussed in the earlier section dealing with compositional dependence of % H (Table VI). For the current sample set, saturates from coal-derived synfuels will tend to be low in n-paraffins and rich in bicyclic saturates. For this reason such samples tend to cluster below the petroleum fuels in Figure 7C. The compound class correlation with V , in Figure 3A is superior to that in Figure 7B. If the regression lines in Figure 7A,C are combined with the specifications SP > 20 mm and Q, > 42.8 MJ/kg, the corresponding % H requirements are closely comparable, viz. % H > 13.40 or > 13.32, respectively. The vertical line drawn in Figure 7 is equivalent to % H = 13.40. This intersects at SG-' = 1.200, which is close to the specification of SG-l > 1.1908. The intersection with the V, correlation is also seen to be in reasonable qualitative accord with the V , < 20 vol % specification. Implications from current % H data are therefore in reasonable accord with earlier work.14 The compositional domain defined by % H > 13.40, as shown in Figure 6, is very similar to the domains defined by Q, > 42.80 MJ/kg and SP > 20 mm. Although not yet a manditory requirement for aviation turbine fuel, a measured hydrogen content of 13.8 w t % or greater is considered sufficient for
Energy & Fuels, Vol. 1, No. 5, 1987 447
Book Reviews
SPECIFICATION DOMAIN
IBCl
IAr 1
Figure 8. Hydrotreating and blending routes to specification quality kerosene fuels. Point A corresponds to a coal-derived syncrude that, when severely hydrotreated, yields the specification quality fuel designated by point C. Alternatively, the coal syncrude could be less severely hydrotreated (to point B) and blended with an appropriate fuel (point D) to yield a specification quality product (point E).
the determination of aromatics, olefins, heat of combustion, and smoke point to be waived in some existing specificat i o n ~ . ~ ~ ~ ~ ~ Refining Coal Hydroliquefaction Syncrudes. Identification of the compositional domain in Figure 5F, which, within the limitations discussed above, is determined by jet fuel property specifications, satisfies one of the main objectives of the current work. The shaded areas in Figures 5 and 8 are the target hydrocarbon compositions (25) SpecificationNo. DERD 2494 (Issue9) for Aviation Turbine Fuel, [NATO F-351, Ministry of Defence, U.K., June 1983. (26) Specification DEF (AUST) 5208A for Aviation Turbine Fuel, [NATO F-351, Australian Commonwealth Department of Defence, October 1985.
that must be achieved in any viable refining strategy. This constraint forms the basis for an improved conceptualization of possible routes toward acceptable quality fuels. The data set used to derive this view (see Experimental Section) is primarily petroleum based, with substantial contributions from coal products and minor contributions from shale oil and peat products. In the following we will focus on coal products. Coal hydroliquefaction syncrudes differ in composition depending on process characteristics. In general, however, such syncrudes (and the kerosene cuts derived therefrom) will tend to occupy the bottom right-hand corner of Figure 8 (e.g. point A). The simplest and most commonly applied route to acceptable jet fuel quality is hydrotreatment. This can be represented by a horizontal line passing from A to C in Figure 8. Clearly this implies the need for very severe hydrotreatment, almost to the point of total extinction of aromatics (point C). A second route, involving less severe hydrotreatment, is also shown in Figure 8. If a suitable blend stock (e.g. Point D in Figure 8) is available, this can be blended with a partially hydrogenated coal product B to yield an acceptable fuel E. The correlations in Tables II-IV that gave rise to Figure 8 are advantageous in that they provide the means for identifying plausible blend stock pairs and for predicting the requisite blend ratios. Current work is directed toward testing the quantitative efficacy of the methods described herein for dealing with synfuels and synfuel blends. Acknowledgment. We thank personnel of the BHP Petroleum Laboratory for assistance. Support for this work was provided under the National Energy Research Development and Demonstration Program, administered by the Australian Commonwealth Department of Resources and Energy. We thank the Broken Hill Proprietary Co., Ltd. for permission to publish this work.
Book Reviews Alternative Energy Sources VI. Volumes 1-4. Edited by T. Nejat Veziroglu (University of Miami). Hemisphere: New York. 1985. 2385 pp. $388.00. ISBN 0-89116-427-8. This four volume set contains the proceedings of the Sixth Miami International Conference on Alternative Energy Sources held in December 1983. In these books, alternative means alternative to petroleum. The set consists of review articles covering most alternative energy sources and was produced directly from the authors' typescript. The production is unusually good for this format. Volume 1and half of Volume 2 deal loosely with solar energy with the topics including photovoltaics, solar collectors, energy storage, and building energy analysis. Volume 2 also contains two articles on biomass energy sources and energy from waste. Articles on wind, fission, fusion, hydrocarbon fuels, combustion, and hydrogen fuel all are contained in Volume 3. Volume 4 deals with conservation, environmental, and planning/management issues. In the areas of this reviewers expertise, the quality of the articles varied enormously. Some were thoughtful, serious evaluations of an area; others contained dogmatic statements of opinion and ignored all conflicting observations. This set might prove a useful
library acquisition for institutions concerned with the broad range of alternative energy technologies.
John W. Larsen, Lehigh University Emerging Clean Coal Technologies. By Engineering & Economics Research, Inc., et al. Noyes Publications: Park Ridge,
NJ. 1986. 293 pp. $36.00. This text is drawn from an interesting Supplemental Report to Congress on Emerging Clean Coal Technologies,dated August, 1985, and prepared by Engineering & Economics Research, Inc.; Hagler, Bailly & Company, Inc.; PEI Associates, Inc.; and Paul W. Spaite, consultant for the U. S. Department of Energy. The authors have divided the emerging technologies into three classes: those intended to provide better protection of the environment, to provide fuel, or to provide energy. The technologies were initially evaluated in terms of environmental performance, technical maturity, applicability, and cost effectiveness. The methodology for each of these evaluations is covered in the first 50 pages. The first appendix then examines the 13 technologies in turn. They are as follows: flue gas cleanup, fluidized-bed combustion, surface coal gasification, advanced coal cleaning, coal-fueled diesel engines, coal-fueled gas turbines, advanced combustors, alternate fuels, fuel cells, coal liquefaction, underground coal gasification, hot gas cleanup, and magnetohydrody-
