Energy & Fuels 1992, 6 , 72-76
72
the errors incurred by the conventional measurement of these data. We found them in the order of f l - 2 % when we tested this method with Boelhouwer’s data.g We also derived a correlation using refractive index instead of specific gravity for the calculation of MW from AEBP. This may be of advantage when only small samples are available. The equation is of the same type as the others: MW = 145 32.5 X 10-7(AEBP3/R15) (7)
+
We applied it to 107 data of distillates from 10 different crude oils published by Boelhouwer and Waterman9 and to 35 petroleum fractions by Kurtz et al.1° Both groups of authors did not provide boiling points but only MWs,
E.
(9) Boelhouwer, C.; Waterman, H. I. J . Inst. Pet. 1953, 40, 116. (10) Kurtz, S. S.; King, R. W.; Stout, W. J.; Partikian, D.G.; Skrabek, A. Anal. Chem. 1956,28, 1929.
densities, and refractive indices. Therefore, we had first to calculate the AEBPs from the experimental MWs and densities. Only then could we derive the correlation between AEPB, MW, and refractive index. The results, shown in Figure 9, are quite satisfactory. With our correlations, eqs 4-7, we believe to have improved eariler means to calculate MWs of petroleum distillates from their mid-boiliig points and specific gravities. By applying them to atmospheric residue fractions obtained by molecular distillation, we have doubled the range from a previous upper limit of under 450 to 950 MW, or from about 1000 to over 1300 O F AEBP.
Acknowledgment. We are grateful to Chevron Research and Technology Co. for allowing publication of this paper. We also acknowledge very helpful comments from a reviewer. Registry No. H2, 1333-74-0; C, 7440-44-0.
Composition of Heavy Petroleums. 4. Significance of the Extended Atmospheric Equivalent Boiling Point (AEBP) Scale Mieczyslaw M. Boduszynski* Chevron Research and Technology Company, Richmond, California 94802
Klaus H. Altgelt Consultant, 555 Appleberry Dr., San Rafael, California 94903 Received July 8, 1991. Revised Manuscript Received September 19, 1991
The first two papers in this series (Energy Fuels 1987,1, 2; 1988,2,597) discussed the variation of the chemical composition of heavy petroleum fractions with increasing atmospheric equivalent boiling point (AEBP) up to about 760 “C (1400 OF). The third paper (this issue) described three correlations developed for the calculation of AEBPs from molecular weight and one more measurement, either specific gravity or H/C ratio or refractive index. In this paper we discuss the value of extending the AEBP scale to encompass the entire heavy crude oil, down to the “bottom of the barrel”. The AEBP distribution curves, extending up to approximately 1650 “C (3000 OF),allow the comparison of heavy petroleums and their fractions on a common, rational basis. We present data for several heavy crude oils to demonstrate the continuity of changing petroleum composition as a function of AEBP. Such continuity of change is important when interpolating or extrapolating physical and chemical properties of petroleum fractions. It also provides decisive clues in the interpretation of analytical measurements performed on “heavy end” fractions.
Introduction
Distillation is the most important separation process used in petroleum refining. It fractionates crude oils and intermediate process streams into various distillates (cuts) based on differences in volatility. These cuts are typically described in terms of boiling point ranges. Each cut is a complex mixture of molecules which cover a given boiling point range. No two crude oils are alike, and even successive tanker loads of the same crude oil often differ. These differences can be frequently revealed by distillation. The so-called “distillation assay” provides a description of the oil composition in terms of yield as a function of boiling point. The distillation assay can be obtained by the actual dis0887-0624/92/2506-0072$03.00/0
tillation or by simulated distillation (SIMDIS).However, conventional distillation assays are limited to petroleum fractions boiling up to about 600 “C (1100 O F ) atmospheric equivalent boiling point (AEBP). When one of us1 introduced the concept of AEBP, the intent was already then to have the concept span the entire composition of crude oil, beyond the boiling range to include the “nondistillable” portion of residua. At the time there did not seem to be a good method for the calculation of AEBP from molecular weight data. Now, having a reliable correlation3 between AEBP on the one hand and (1) Boduszynski, M. M. Energy Fuels 1987, 1, 2-11. (2) Boduszynski, M. M. Energy Fuels 1988, 2, 597-613.
0 1992 American Chemical Society
Energy & Fuels, Vol. 6, No. 1, 1992 73
Composition of Heavy Petroleums MW plus specific gravity (sp gr) or MW plus H/C ratio on the other hand, we can proceed with this extension. In this paper, we present the entire AEBP scale which now extends to about 1650 "C (3000 OF). By example of data obtained from several heavy crude oils we demonstrate the continuity of changing petroleum composition as a function of AEBP. Experimental Section Atmospheric residues (AR's, -650 O F + AEBP) were derived from five different heavy crude oils: Arabian Heavy (27.7 API), Offshore California (22.5 API),Maya (22.2 API), Kem River (13.6 API),and Boscan (10.1API). More details on these samples can be found in the earlier papers in this series.'V2 The experimental methods, fractionation by distillation and sequential elution fractionation (SEF),as well as simulated distillation by GC and by vacuum thermal gravimetric analysis (VTGA), and molecular weight determination by vapor phase osmometry (VPO),have also been described before.'V2
"Almospherlc" DlSllllalio"
'Vacuum"
Dlatlllatlon
Vacuum ResldYe
"MOIecuIar" Dlatlllatlon (DISTACT) 1
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I
I
SOIUMI1t Fmcllo~t~n ISEF.1 Swuentlal Elullon Fractionition)
.
I
-AET TBP
I
.
__L
AEBP
4
Figure 1. Distillates and solubility fractions on the AEBP scale.
Results and Discussion The Extended AEBP Scale. The physical and chemical properties of petroleum distillates are known to change gradually with increasing boiling point. The earlier papers in this series'3 demonstrated that, whenever the distillable range was expanded, first beyond the limit of atmospheric distillation (1300 OF AEBP) is deposited in a thin film onto small particles of inert support material (Chromosorb T) which is packed in a column and extracted with a series of solvents.'V2 The underlying principle of both of these methods (DISTACT-volatility separation and SEF-solubility separation) are the various molecular interactions, the van der Waals forces. The dispersion forces are proportional to the surface area of the interacting molecules and thus, for paraffins and highly alkylated aromatics, they are approximately proportional to molecular weight. For the much more complex types of molecules expected in nondistillable residua the trend toward greater dispersion forces with higher molecular weight remains, although the proportionality is no longer maintained. Quite generally,
as the molecular size increases, the dispersion forces increase, and so does the boiling point and so does the solubility ~ a r a m e t e r . ~Therefore, ?~ for each compound type the basis of the separation is ultimately the molecular weight. This is true for both distillation and methods involving solubility. Thus, the basis for the separation remains the same in going from volatility separation (by DISTACT) to solubility separation (by SEF) even if in detail the separations will differ. Complicating this situation is the fact that the molecules in nondistillable residua are so complex that here we cannot really distinguish compound types as is possible in low and middle distillates. The equivalency of solubility separation and distillation still holds even though these materials cannot be distilled. In fact, the average molecular weight of our SEF fractions always increases with decreasing solubility (from SEF-1 to SEF-4 fractions). Figure 1illustrates how the different crude oil fractions fit into the scheme of the AEBP scale. Now the question is how to convert molecular weights into AEBPs. While for many purposes the boiling range is of primary interest, for others, especially for detecting and demonstrating trends, a single data point is preferable. Such a convenient single number for complex fractions is the mid-boiling point or, in our more general terms, the mid-AEBP. The mid-AEBP of a distillate is the 50% mass point on an AEBP distribution curve which is best established by simulated distillation. In case of solventderived SEF fractions, the mid-AEBP is a hypothetical value which can be calculated using one of the following equation^:^
(3) Altgelt, K. H.; Boduszynski, M. M. Composition of Heavy Petroleums, 3. An Improved Boiling Point - Molecular Weight Relation Energy Fuels, preceding paper in this issue.
(4) Hildebrand, J.; Scott, R. Solubility of Non-Electrolytes, Reinhold; New York, 1949. (5) Hanson, C. M. Ind. Eng. Chem., Prod. Res. Deu. 1969,8, 2.
(Mn- 170)(H/C)O.'
mid-AEBP ( O F ) =
I 1
113
2.67
where M,, is the number-average molecular weight, sp gr the specific gravity, and H/C hydrogen to carbon atomic ratio. One could argue, if we accept the molecular weight as the basis of interconversion between distillates and solvent-derived SEF fractions, why not use a molecular weight scale directly instead of the more complicated
Boduszynski and Altgelt
74 Energy & Fuels, Vol. 6, No. 1, 1992 1000,
v Offshore California 0
4
500,
,
1000 , ’ ’
’
’
Kern River
’
’
’
’ 1500 ’ ’ ’ ’ 2000 ’ ’ ’ ’ 2500 ’ ’ ’ ’ 3000 ’
Mid Atmospheric Equivalent Boiling Point, “F
Figure 2. Crude oil AEBP distribution curves.
AEBP scale? The answer is, yes, a molecular weight scale would be scientifically cleaner than the “boiling point” scale in that it would completely exclude variations arising from differences in chemical composition. However, as we said earlier, distillation is such an important separation process in petroleum refining, and the concept of boiling point scale is so widely used that it should have a similar place in petroleum analysis in general and for the categorization and comparison of petroleum samples in particular. The AEBP Distribution Curves for Heavy Crude Oils. Figure 2 shows the plots of cumulative weight percent of the fractions versus their mid-AEBPs (“cumulative assays”) for three heavy crude oils: Kern River, Offshore California, and Boscan. Note the striking ‘ 4 smoothness of the curves. It points out two things: (1) the value of using the mid-AEBPs for the fractions as a variable and (2) the consistency of the data across the entire AEBP range. Interestingly, the AEBP distribution curves reveal that the “less heavy” (22.5 API gravity) Offshore California crude oil contains more material in high AEBP fractions than the “heavier” (13.6 API gravity) Kern River. The great advantage of the AEBP scale is the possibility to compare whole crude oils, including their nondistillable residua, on a common, rational basis. Chemical Properties of Heavy Petroleums as a Function of AEBP. The hydrogen deficiency of a molecule is usually expressed in terms of the socalled “2” number (hydrogen deficiency value) in the general formula C,H,+ZX (where C is carbon atom, H hydrogen atom, and X heteroatom). The average 2 values for distillate cuts and solvent-derived SEF fractions were calculated using results of elemental analysis and number-average molecular weights. Figure 3 illustrates changes of hydrogen deficiency with increasing AEBP for five crude oils. Note the dramatic increase of hydrogen deficiency (negative 2 increases, log scale) as the AEBP increases. Interestingly, the curves for all five crudes follow a smooth and common pattern. Figure 4 illustrates the changes in the average number of sulfur atoms per molecule with increasing AEBP for AR’s (atmospheric residues) which were derived from five different crude oils. The sulfur distribution curves again are remarkably smooth over the entire range. They reveal significant differences between Kern River and the other crudes. The low-sulfur Kern River AR (1.20 w t % S) has only about 1sulfur atom in 10 molecules at -700 OF, while at -2000 OF, on average, every molecule contains one sulfur atom. The curves for the other four crudes form a narrow band revealing one sulfur atom per molecule at
t Maya AR -4-
Arabian Heavy AR
+ Boscan
AR
+ Offshore Cllifomia AR
K)
Mid Atmospheric Equivalent Boiling Point (OF) Figure 3. Average hydrogen deficiency value 2 as a function of AEBP.
1 1.20 WI% S in AR t Maya 4.17 W1% S in AR -4-
Arabianlieavy
4.36 W19.S in AR
+ Boscan 5.94 WI% S in AR
r Y/‘
J
0
0
500
1000
1500
2 3
2500
3 00
Mid Atmospheric Equivalent Boiling Point ( O F Figure 4. Average number of sulfur atoms per molecule as a function of AEBP.
-1200 O F , three at -1600 OF, six at -2000 OF, and up to about 1 2 at -2600 O F AEBP. The plots representing an ”average number” of nitrogen atoms/molecule at a given mid-AEBP are shown in Figure
Composition of Heavy Petroleums
Energy & Fuels, Vol. 6, No. 1, 1992 76
! +- Offshore Cdlfomb
.
.. .......... ... ..... ... ....... ........
,
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l
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am Wt% N l n AR
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Figure 6. Micro carbon residue as a function of AEBP. 1600
0
500
loo0
1500
2000
2500
:
Mid Atmospheric Equivalent Boiling Point (OF) Figure 5. Average number of nitrogen atoms per molecule as a function of AEBP.
5. Again, data for all five crudes show smooth distribution patterns over the entire AEBP range. The average number of nitrogen atoms/mdecule increases rapidly with increasing AEBP for all five crudes. For example, in the nitrogen-rich Offshore California crude oil (0.83w t % N in AR), at -700 OF AEBP approximately 6 molecules in 100 contain a nitrogen atom. At -1600 O F AEBP, on average, every molecule in this crude oil contains a nitrogen atom. At -2700 O F AEBP, there are almost nine nitrogen atoms/molecule in this crude oil. Our low-nitrogen Arabian Heavy crude oil (0.25 wt % N in AR) has only about 1 nitrogen-containingmolecule in 100 at -700 OF AEBP. At -1600 O F AEBP, about every other molecule contains a nitrogen atom, and at -2600 O F AEBP there are 3.6 nitrogen atoms/molecule even in this crude oil. The pattern of oxygen-containingmolecules is similar to that of the nitrogen compounds. Although the actual distribution of sulfur and nitrogen in any one molecule is not known, the observed rapid increase in heteroatom concentration with increasing AEBP indicatesa high concentrationof compounds having several heteroatoms per molecule. These data illustrate the immense complexity of "heavy ends" of petroleum. We hope that these results clarify the challenges facing petroleum chemists, attempting to unravel the molecular structure of those species. We have demonstrated so far that such important chemical properties as hydrogen deficiency and concentrations of sulfur and nitrogen all exhibit smooth distribution curves which extend over the entire AEBP range. High hydrogen deficiency and high concentrations of heteroatoms are usually associated with the tendency of the feedstock to form "coke". The coking propensity of feedstocks is commonly measured using the ASTM D 4530 microcarbon residue (MCR) method, or older methods such as Conradson or Ramsbotton carbon residue. In Figure 6,we have plotted the MCR results for the five selected crude oils. Again, the plots exhibit smooth dis-
Figure 7. Distribution of metals in Offshore Califomia crude
oil.
tribution patterns over a wide AEBP range. Data for all five crudes show the MCR increasesrapidly with increasing AEBP. Organometallic compounds in petroleum contain predominantly vanadium, nickel and to a lesser extent, iron. Concentrations of these metals in crude oils vary from less than 1 ppm to several hundred ppm depending on the metal and on crude oil origin. The distribution of metals in heavy crude oils is of particular interest because metals are harmful to most existing catalytic processes and must be removed before heavy crudes or resids can be effectively converted to low boiling transportation fuels. Figure 7 illustrates the distribution of vanadium, nickel, and iron in Offshore California crude oil. The plots show changes in metal concentrations with increasing AEBP. Appreciable concentrationsof metals appear above loo0 O F AEBP (vacuum residue portion). AU three metals (V, Ni, and Fe) exhibit distribution patterns with distinct "humps" around -1200 OF AEBP followed by a rapid increase in concentration with increasing AEBP. Vanadium is the most abundant (364ppm in AR) of the three metals and exhibits this bimodal distribution pattern most clearly. The other four of our crudes have very similar metal distribution patterns.
-
76
Energy & Fuels 1992,6 , 76-82
Conclusions We have demonstrated that a concept of atmospheric equivalent boiling point (AEBP) can be extended from a volatility separation (distillation) to a solubility separation (SEF, sequential elution fractionation). The extended AEBP scale encompasses the entire “boiling range” of petroleum, including hypothetical AEBP ranges of nondistillable residue fractions. The AEBP distribution curves, extending up to approximately 1650 OC (3000 OF), allow the comparison of entire heavy petroleums and their fractions on a common, rational basis. We have further demonstrated the continuity of changing petroleum composition as a function of AEBP. Such continuity of change is important when interpolating or extrapolating physical and chemical properties of petroleum fractions. It also provides decisive clues for the choice and the interpretation of analytical measurements performed on “heavy ends” fractions. We think the principle of AEBP is sound, but some of
the underlying separation and measuring techniques can stand improvement. For example, one aspect needing attention is that of measuring a correct number-average molecular weight for solvent-derived (SEF) fractions. So far, VPO measurements of such fractions in the polar solvent pyridine at 90 “C give results 2-3-fold lower than those obtained by measurements in toluene.2 However, even these may still be too high and may thus inflate the calculated mid-AEBPs. The rapid progress in supercritical fluid extraction (SFE) offers a new way for the solubility fractionation of nondistillable residua, and supercritical fluid chromatography (SFC) as a SIMDIS method may provide the means for a direct measurement of AEBP’s for solubility fractions.
Acknowledgment. We express our appreciation to R. J. Clay for his assistance in plotting the data. We are also grateful to Chevron Research and Technology Co. for supporting this work and allowing publication of this paper.
Characterization of Synthetic Gasoline from the Chloromethane-Zeolite Reaction Curt M. White,* Louise J. Douglas, Joseph P. Hackett, and Richard R. Anderson Indirect Liquefaction Division, Pittsburgh Energy Technology Center, P.O. Box 10940, Pittsburgh, Pennsylvania 15236 Received August 15, 1991. Revised Manuscript Received September 24, 1991
Products from the reaction of chloromethane with a zeolite have been characterized using highresolution gas chromatography combined with either mass spectrometry or Fourier transform infrared spectroscopy. Hydrocarbon gases having four carbons and less were about 53 wt 9% of the total product. A condensed liquid product constituted about 47 wt 9% of the product. Over 240 compounds were analytically separated from the condensed liquid product by gas chromatography, allowing the identification of 106 products that constituted about 89 wt 9% of the condensed liquid product. Acyclic and cyclic alkanes and olefins, as well as aromatics, make up the majority of the condensed liquid product, which contained compounds having carbon numbers up to 13. Chloroalkanes, also found in the product, are thought to arise from addition of hydrogen chloride to olefins. Hydrocarbon products from the reaction of chloromethane and zeolite are qualitatively similar to those from the reaction of methanol and zeolite, although the isomer distribution was quantitatively different among the polymethylbenzenes. 1,2,4-Trimethylbenzene was the major organic product, constituting 45 wt 9% of the condensed liquid product. Hydrocarbon products containing four carbons and less were analyzed using a porous layer open tubular column coated with Al,O,/KCl. The alumina stationary phase reacted with 2-chloropropane to form propene. Reaction of the stationary phase with the analytes limits the use of alumina columns for characterization of products from this reaction. The chloromethane, produced in the first step of the Introduction process by oxyhydrochlorination of is subseThe conversion of both methane and methanol to gasoline-range hydrocarbons is of great commercial and eco(I) Fox,M. J.; Chen, T.-P.; Degen, B. D. Direct Methane Conoersion nomic importance. Conversion of methane to methanol Process Evaluations. Bechtel National, Inc., July, 1988. Prepared for on a commercial scale is accomplished by first the US. Department of Energy under contract No. DEAC22-87PC79814. it to carbon monoxide and hydrogen, followed by reduction (2) Noceti, R. P.; Taylor, C. E. United States Patent 4,769,504, Sept. of the carbon monoxide to methanol. Since methane can 6,1988. (3) Taylor, C. E.; Noceti, R. P.; Schehl, R. R. In Methane Conuersion; be converted to in One this may be Bibby, D. M., Chang, C. D., Howe, R. F., Yurchak, S., Eds.; Elsevier: a viable alternative to the methanol-to-gasoline process.’ Amsterdam, 1988; pp 483-489. (4) Taylor, C. E.; Noceti, R. P. Catalysis Theory and Practice, ProIn the Pittsburgh Energy Technology Center’s methaneceedings 9th Congress On Catalysis; Phillips, M. J., Ternan, M., Eds.; to-gasoline &loromethane is the intermediate in Institute of Canada: Ottawa, Canada, 1388; Vol. 2. the conversion of methane to a high-octane liquid f ~ e l . ~ - ~The(5)Chemical Pieters, W. J. M.; Conner, W. C.; Carlson, E. J. Appl. Catal. 1984, 1I, 35-48.
* Author
to whom correspondence should be addressed.
(6) Conner, W. C.; Pieters, W. J. M.; Gates, W.; Wilkalis, J. E. Appl. Catal. 1984, 11, 49-58.
This article not subject to U.S. Copyright. Published 1992 by the American Chemical Society
