Energy & Fuels 1992,6, 581-585
581
Observed and Predicted Properties of Jet and Diesel Fuels Formulated from Coal Liquefaction and Fischer-Tropsch Feedstocks David J. Cookson and Brian E. Smith' BHP Research-Melbourne Laboratories, 245 Wellington Rd., Mulgrave, Victoria, 31 70, Australia Received October 15, 1991. Revised Manuscript Received May 26, 1992
A simple, chemically explicit tool for guiding blending options has been tested and verified for jet and diesel fuels of fixed boiling range, deriving from Fischer-Tropsch synthesis, coal hydroliquefaction, and petroleum sources. The complementary nature of the properties of Fischer-Tropsch and coal hydroliquefaction fuels has been demonstrated. The approach described utilizes previously derived fuel composition-property relationships of the form P = al[nl + a2EBCI + as[ArI, where P is the property in question, In], [BCI, and [Arl are the weight fractions of n-alkanes, branched plus cyclic saturates, and aromatics, respectively, and al, a2, and a3 are coefficients of known value from previous studies of diverse fuels. The methodology has proven effective in identifying suitable blendstocks, estimating suitable blend ratios, and calculating blend properties. It has been applied to jet fuel smoke point, aromatics content, hydrogen content, heat of combustion, freezing point, and specific gravity, as well as to diesel fuel pour point, cloud point, hydrogen content, specific gravity, aniline point, diesel index, cetane index, and cetane number. The successful application of this methodologydoes not require that the propertiesof the blendstocks themselves are accurately predicted or that the blend properties are linear combinations of blendstock properties. Introduction There are many examples in the literature of the use of physical and chemical property data,or spectroscopicdata, to calculate jet or diesel fuel properties (see, for example, refs 1-18). The equations used in the present work are distinctive in that they relate fuel compositions to properties in a manner that is extremely simple and is readily comprehensiblein chemical terms. These relationships are valid for jet and diesel fuels of specific boiling ranges (190-230 and 230-320 OC, respectively) and were
* To whom correspondence should be addreseed.
(1)Significance of Tests for Petroleum Products; Boldt, K., Hall, B. R., Eds.; 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)Solash, J.; Hazlett, R. N.; Hall, J. M.; Nowack, C. J. Fuel 1978,57, 521-528. (4)Petrovic, K.; Vitrovic, D. J. Inst. Pet. 1973,59,20-26. (5)Gulder, 0.L.;Glavincevski, B.; Des, S. J. Eng. Gas Turb. Power 1989,111,77-83. (6)Ramaswamy, V.; Singh, I. D. Fuel 1990,69,122-123. (7)Kalasinsky, K. S.;Minyard, Jr., J. P.; Kalasinsky, V. F.; Durig, J. R. Energy Fuels 1989,3,304-307. (8) Reddy, S. R. Fuel 1986,65,1647-1652. (9)Gulder, 0.L.; Glavincevski, B. Ind. Eng. Chem. Prod. Res. Deu. 1986,25,163-156. (10)Gulder, 0.L.;Glavincevski, B. Combust. Flame 1986,63,231238. (11)Bailey, B. K.; Russell, J. A.; Wimer, W. W.; Buckingham, J. P. Cetane Number Prediction from Roton-Type Distributionand Relative Hydrogen Population; SAE Technical Paper Series 861521,1986. (12)Caswell, K. A.; Glass, T. E.; Swann, M.; Don, H. C. Anal. Chem. 1989,61,206-211. (13)DeFries, T. H.; Indritz.. D.;. KastruD. _ .R. V. Ind. Ena. - Chem. Res. 1987,188-193. (14)Colliins, J. M.; Unzelman, G.H. Oil Gas J. 1982,148-160. (15)Cookson.. D. J.:. Latten.. J. L.:. Shaw.. I. M.:. Smith. B. E. Fuel 1985. 64,509-519. (16)Cookson, D. J.; Lloyd, C. P.; Smith, B. E. Energy Fuels 1987,I, 438-447. (17)Cookson, D. J.; Lloyd, C. P.; Smith, B. E. Energy Fuels 1988,2, 854-860. (18)Cookson, D. J.; Smith, B. E. Energy Fuels 1990,4,152-156.
0887-0624/92/2506-0581$03.00/0
derived1&18from a sample set including many petroleum and synfuel samples of diverse origins. Thus, relatively simple and rapid measurement of composition by HPLC and either GC or NMR1&17or by NMR alone18 allows prediction of, for example,jet fuel smoke point and freezing point or diesel fuel cetane index and cloud point. These composition-property relationships can be used16 as an aid in devising and comparing fuel refining routes, including blending options. With regard to blending, potential blendstocks can be identified, suitable blend ratios can be estimated, and the property values of the resultant blends can be calculated. In the present paper the utility of simple composition-property relationships in guiding blending strategies is tested for the first time. The focus of this paper will be on blendstocks of special interest, viz., coal hydroliquefaction and Fischer-Tropsch fuels. It is well-known that coal hydroliquefaction and Fischer-Tropsch fuels tend to have complementary properties (see within). Other workers1g*2'J have proposed a combination of coal hydroliquefactionand Fischer-Tropsch synthesis as an effective route to syntheticfuels on the basis of product fuel quality and/or process benefits. In this regard methane (asnatural gas) may offer some special process advantages if used as the source of syngas for Fischer-Tropsch synthesis. Methane is inherently hydrogen rich/carbon poor and thus, in principle, complements coal, which is comparatively hydrogen poor/carbon rich. We are not aware of the existence, in the open literature, of comparabledata to that presented herein, concerning coal hydroliquefaction and Fischer-Tropsch blends, or of any (19)Imhausen, K.-H. Conversion of Australian CoalsintoLiquid Fuels; Joint AustralidFederal Republic of Germany Feaeibility Study, 1981. (20)Pollock,.D. C. Future Plans for Liquid Fuels and Advanced (Catalytic) GasaficationlFuel Cell System at Great Plaine Gasification Plant; presented at Joint Australian/USA Workshop on Low Rank Coals, Billings, Montana, May 1991,proceedings in preparation.
Q 1992 American Chemical
Society
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582 Energy & Fuels, Vol. 6, No. 5,1992
attempt to apply fuel composition-property relationships to such a blending exercise.
A.
Experimental Section Sample Origins. The jet and diesel fuels used in this study have been obtained from three source types: coal liquefaction, Fischer-Tropsch synthesis, and petroleum products. The principal coal-derivedfuels used in this study are the products of two distinctivemultiple-cycle continuouscoal hydroliquefactiontrials with Wandoan (subbituminous,SE Queensland)coalon the BHP Research bench-scalereactor.21) Both trials (designated CR162 and CR165)employed a disposableiron ore catalyst in the primary liquefaction stage (stagel), while a solvent rehydrogenationstep (stage2) was used in only one trial (CR165). Liquefactionreaction conditions were 450 "C and 25 MPa with a nominal slurry residence time of 35 min. The wide boiling range syncrude products from CR162 and CR165were subsequentlyhydrotreated over a Ni/Mo/A1203 catalyst (Shell 424, trilobe). The hydrotreated product oils, designated CR208/1, CR208/8,and CR208/ 10,were the result of processing under the following conditions: 395 "C, 22 MPa and 0.33 h-l liquid hourly space velocity;375 "C, 22 MPa and 0.83 h-1; and 396 "C, 18MPa and 0.81 h-l, respectively. Jet and diesel fuel products boiling in the ranges 190-230 and 230-320 OC, respectively, were distilled from the hydrotreated oils. Additionalcoal derived fuels,designated CR121and CR159, were produced in a similar fashion from Rosedale (lignite, Latrobe Valley, Victoria) and Wandoan coals. The two Fischer-Tropsch fuels (designatedFT) were produced on the fixed-bedFischer-Tropsch reactor at BHP Research using a feed gas consisting of a 2:l molar ratio of hydrogen and carbon monoxide. Details of reaction conditions have been presented elsewhere.22The Fischer-Tropsch fuels contain minor amounts of monoolefins (ca. 3-4%)22which have been accounted here as n-alkanes. The six petroleum-derivedfuels were obtained from the followingfive Australiansources: CarnarvonBasin (1);Cooper Basin (1);Gippsland Basin (2); Eromanga Basin (1);Canning Basin (1). The petroleum sources are designated Pl-P5 respectively. Analytical Methods. Compositionsof the jet and dieselfuels, expressedin terms of the weight fractions of n-alkanes,branched plus cyclic saturates, and aromatics were determined using highperformance liquid chromatography (HPLC) as well as nuclear magnetic resonance (NMR)spectroscopy. These procedureshave been described in detail elsewhere.16J7va Normal alkanes are manifest in 13CNMR as relatively sharp, prominent resonances which are readily integrated to yield the weight fraction of nalkyl carbon (Cn)which closely approximatesthe weight fraction of n-alkanes ([ n]).16J8,22Cnvaluesof K0.15 are difficultto measure accurately due to resonance overlap. In such cases where resonance intensity cannot be attributed unambiguously to nalkyl carbon, a zero value of C, is assigned.18 This is the case for all coal-derived fuels used in this study. HPLC resolves saturates, monoaromatics, diaromatics, and polynuclear aromatics. Integration, together with use of appropriate response factors determined in earlier yields the appropriate weight fractions of these species. In the current work, mono-, di-, and polynuclear aromatics are grouped as one class, namely,aromatics. The abundance of branched plus cyclic saturates is simply obtained as the difference between the weight fraction of saturates (from HPLC) and the weight fraction of n-alkanes (from NMR). Carbon aromaticity, C, is the fraction of total 13CNMR intensity attributable to aromatic carbon (110160 ppm). In conjunction with NMR measured n-alkyl carbon content (Cn),C, provides a simple,alternative measure of sample aromaticity which can be used in composition-property relationships.la Fuel Testing Procedures. Unless otherwise specified, all fuel tests were carried out by the BHP Petroleum Laboratory (21) Bien, C. N.; Luttin, K. P.; Smith, B. E.; White, N. Energy Fuels igaa,2,807-815. (22) Cookson, D. J.; Smith, B. E. Fuel 1989,68, 776781. (23) Cookson, D. J.; Smith, B. E.; Shaw, I. M. Fuel 1987,66,758-765.
Figure 1. Compositionsof (A) jet fuel and (B)diesel fuel blendstocks and blends used in this study. The vertices of each triangular diagram correspond to 100 wt % abundance of nalkanes [n] ,branched plus cyclic saturates [BC],and aromatics [Ar]. The shaded regions in each diagram represent the compositionalrequirementsfor (A)jet fuelsto meet specifications for smoke point (>20 mm), net heat of combustion (>42.80 MJ/ kg), aromatics content (20 mm), aromatics content (45) specifications taken from the appropriate Australian Standard.29 The principal coal-derived jet and diesel fuels used as blendstocks in this study were distilled from three hydrotreated coal liquefaction syncrudes. Hydrotreating severity decreased in the order CR20811 > CR208/8 > CR208/10 as indicated by their relative positions in Figure 1. The Fischer-Tropsch fuels are composed predominantly of n-alkanes (ca. 90 w t %), with smaller concentrations of branched plus cyclic saturates.22 Such fuels were identified in earlier work16as prospective blendstocks on the basis of their composition. Compositions and properties of all blendstocksand blends are given in Tables I and 11. In a ternary composition diagram all binary blends can be represented by a straight line joining blendstock points. The relative proportions of blendstocks are inversely related to the lengths of the relevant blend line segments. Thus, in Figure 1A for example, BJ2 contains 25% FT and 75% CR208/8. Four jet fuel blends (designated BJ1-BJ4) and three diesel fuel blends (designated BD1-BD3) were prepared (Figure 1and Tables I and 11). BJ1 was formulated to lie in the specification domain region for jet fuels. BJ2 uses a less severelyhydrotreated coal liquefaction fuel (CR208/ 8) and was intended to be borderline in quality. Figure 1A suggests that FT and the least severely hydrotreated coal liquefaction product, CR208/10, cannot be blended in any ratio to meet all specifications. BJ3 and BJ4 were prepared to test this proposition. Diesel fuel blends, BD1 and BD2 (Figure 1B and Table 111, were formulated from the Fischer-Tropsch diesel fuel and the two most severely hydrotreated coal liquefaction fuels and are expected to
meet quality requirements. BD3was prepared in a manner which would place it closer to borderline quality. Composition-Property Relationships. Compitionproperty relationships to be used in the present work take the form P = al[nl + a2[BCl + a3[Arl (1) where P is the property in question, [nl,[BCI, and [Arl are the weight fractions of n-alkanes, branched plus cyclic saturates, and aromatics, respectively, and a1, a2, and a3 are coefficientsdetermined from multiple linear regression analysis.16J7Values of coefficientsal, a2, and a3 are listed in Table 111. There are limitations on the validity of the models represented in eq 1and Table 111, as noted previously.16J7 These limitations pertain to (i) composition (fuels with compositions outside the range of reference fuels used in the model derivation), (ii) properties (fuelswith observedl predicted properties outside the reference range), and (iii) source (fuelsfrom other than petroleum, coal liquefaction, shale oil, or peat pyrolysis origin). Calculated property values shown in brackets in Tables I and I1 pertain to fuels which lie outside acceptable composition or property constraints. For example, the FT jet and diesel fuels have an exceptionallyhigh n-alkane content which places them well outside the compositional range of the reference f u e l ~ which ~ ~ J tends ~ to be near the shaded specification domains indicated in Figure 1. Also, because the lowtemperature properties of highly naphthenic coal liquefaction fuels proved difficult to measure reliably, these fuels were excluded when deriving equations for jet fuel freezing point and diesel fuel pour point and cloud point.16J7 These fuels are thus outside the acceptable compositional range for freezing point, pour point, and cloud point calculations. This is also the case for the diesel blend BD1. Predicted values shown in brackets in Tables I and I1 cannot be expected to be reliable.
(29) Australian Standard 3576-1988 for Automotive Diesel Fuel; Standards Association of Australia, 1988.
(30)Cookson, D. J.; Smith, B. E.; Johnston, R. R. M. Unpublished results.
584 Energy & Fuels, Vol. 6, No. 5, 1992
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Table 11. Composition and Properties (Observed and Calculated) of Diesel Fuel Blendstocks and Blends. FT CR208/1 CR208/8 CR208/10 BD1 BD2 BD3 specifn coal liquid blendstock blend ratio FTcoal liquid composition [nl, w t % [BCI, wt % [Arl, wt % car, 5% pour point, " C obsd calcd cloud point, "C obsd calcd hydrogen content, wt % obsd calcd specific gravity, 60/60F obsd calcd aniline point, OC obsd calcd diesel index obsd calcd cetane index (BP) obsd calcd cetane index (AP) obsd calcd
CR208/1
CR208/8
CR208/10
20:80
33:67
3862
18.0 80.0 2.0
29.8 53.7 16.5
34.3 34.3 31.4
90.2 9.8 0.0 0.0
0.0 97.5 2.5 0.0
0.0 75.3 24.7 12.1
0.0 49.4 50.6 26.6
3 (21.8)
-33 (-48.7)
-45 (-41.3)
-42 (-33.6)
-21 (-34.6)
-15 -20.4
-12 -11.9
4 (21)
-26 (-42.1)
-28 (-34.3)
-27 (-27.3)
-21 (-29.5)
-12 -16.0
-10 -7.6
15.18 (15.79)
13.15 13.51
12.53 (12.49)
11.71 (11.21)
13.73 13.97
13.50 13.58
13.20 13.00
0.7713 (0.7480)
0.8898 0.8780
0.9070 0.9064
0.9185 (0.9421)
0.8639 0.8485
0.8580 0.8472
0.8555 0.8575
90.8 (110.4)
61.8 59.6
46.0 48.6
26.7 (35.9)
68.6 69.7
64.1 69.0
59.1 64.2
101.4 (133.1)
39.0 41.3
28.0 29.4
18.0 (18.1)
50.2 55.5
49.2 55.5
46.9 49.5
78.5 (91.6)
35.8 37.8
30.9 30.2
24.4 (21.2)
44.3 48.6
46.6 50.4
45.0 48.0
79.3 (93.5)
45.7 47.0
33.9 34.3
24.1 (26.4)
52.1 56.3
47.8 53.9
43.4 47.7
45
Property values in parentheses correspond to those cases where sample composition and/or property values lie outside the ranges used in the original derivation of the model (see text).
Table 111. Three-Parameter Models for Jet and Diesel Fuel Properties (Eq 1). DroDertv
range
a,
a9
as
Jet Fuels smoke point, mm
15-38 1-38 4.1-24.2 45.46-46.94
Table IV. Blending Trials with Petroleum-Derived Jet Fuels.
51.0 47.3 -3.5 44.41
26.1 21.1 4.8 43.33
-30.7 -4.3 91.0 40.18
16.11 -12.7 1.402
13.91 -61.0 1.192
9.64 -50.4 1.053
aromatics content, vol % net heat of combustion, MJ/kg hydrogen content, wt 5% freezing point, O C inverse specific gravity
12.63-14.88 -5Oto-32 1.1459-1.2918
pour point, O C cloud point, "C hydrogen content, w t % inverse specific gravity aniline point, "C diesel index cetane index (BP) cetane index (AP) cetane numbep
Diesel Fuels -51 to 0 29.6 -49.5 -16.1 -38 to 5 28.0 -43.0 -7.6 12.39-14.48 16.02 13.63 9.00 1.0996-1.2442 1.3579 1.1430 0.9819 60.8 11.6 41.5-82.9 115.8 25.6-80.8 b 30.2-64.5 91.4 38.7 4.1 31.2-68.4 98.4 48.4 -8.6 40-71 96.3 50.9 10.4
Coefficients taken from refs 16 and 17 except for cetane number where coefficients are taken from ref 30. Model used is based on predicted values of aniline point (in O F ) and API gravity where API(pred) = (141.5/SG(pred)) - 131.5 as in ref 17.
Results for Fischer-Tropschand Coal Liquefaction Fuel Blends. Experimentally measured property values for the blended jet fuels BJ1-BJ4 are given in Table I together with the predicted values. As expected (see Figure lA), all the property values of BJ1 are within specification. Observed values of smoke point (30 mm) and net heat of combustion (43.24 MJ/kg) are desirably high, whereas values of aromatics content (2.4 vol 5'% ) and freezing point (-46.5 "C) are desirably low. Blend BJ2 (Figure 1A) is close to the borders of the specification domain defined by the requirements for aromatics content and smoke point. Observed values of these properties are marginal,
composition [nl, w t % [BCI, wt % [Arl, wt %
car, 96
P1
P2
P3
Pl/P2
Pl/P3
0.0 82.7 17.3 11.1
56.6 37.1 6.3 2.3
34.0 48.3 17.7 11.5
28.3 59.9 12.8
17.0 65.5 17.5
smoke point, mm obsd 19 37 24 24 20 calcd 26.4 20.4 gross heat of combustion, MJ/kg obsd 45.62 46.88 46.22 46.24 45.94 calcd 46.24 45.82 freezing point, OC obsd
