Energy & Fuels 1992,6,68-72
68
particle size is accompanied by a significant increase in anhydrite content of the sintered ash. The minimum sintering temperature is also the temperature at which the first significant increase in anhydrite is observed. The minimum sintering temperatures determined by the drop tube furnace method are lower than those reported previously using an electrical resistance measurement tech-
nique, suggesting that earlier reports of the minimum sintering temperature that relied on ash prepared at 750 "C are in error by being too high. Acknowledgment. Financial support for this study was provided by the Commonwealth of Pennsylvania under the Coal Water Fuel Project.
Composition of Heavy Petroleums. 3. An Improved Boiling Point-Molecular Weight Relation Klaus H. Altgelt Consultant, 555 Appleberry Dr., San Rafael, California 94903
Mieczyslaw M. Boduszynski* Chevron Research and Technology Company, Richmond, California 94802 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) introduced the concept of extended atmospheric equivalent boiling point (AEBP) to molecular distillates of petroleum residues. In this paper we describe three correlations between AEBP and M,, (number average molecular weight) by means of a third variable, where the latter may be (a) specific gravity, (b) H/C ratio, or (c) refractive index. These correlations, we believe, are better than earlier ones between mid-boiling point, molecular weight (MW), and specific gravity. By applying them to atmospheric residue fractions obtained by molecular distillation we have doubled the range from a previous upper limit of less than 450 to 950 MW, or from about 1000" to over 1300 "F AEBP.
Earlier Correlations Referring to Winn's3 nomographs, Sim and Daubert4 published an equation which relates boiling point, in our terminology AEBP, and specific gravity (sp gr) to molecular weight (MW): MW = 5.805 X 10-5(AEBP'.3776 /sp gr0.9371) (1) We will call this the Winn equation. Two groups modified this relation slightly to make it fit their data more closely. White et al.5proposed eq 2, and Trytten and G r a p eq 3. MW = 4.059 X 10-6(AEBP2.5497 /sp gr1.4002) (2) MW = 2.410 X 10+(AEBP2.847 /sp gr2.130)
(3)
Note that the boiling points of eq 1and 3 are in kelvin ("C 273), those of eq 2 in rankin ( O F 640). We tested the different versions with a set of model compound data published by the Thermodynamic Research Center (TRC) at the Texas A&M University (1989) and a few additional ones taken from the CRC Handbook of Physical and Chemical Data (1990). The compounds consisted of normal and isoparaffins, alkylcyclohexanes
+
+
(1) Boduszynski, M. M. Energy Fuels 1987, 1 , 2. (2) Boduszynski, M. M. Energy Fuels 1988,2, 597. (3) Winn, F. W. The Petroleum Refiner 1957, 36, 157. (4) Sim, W. J.; Daubed, T. E. Znd. Eng. Chem. Process Des. Deu. 1980, 19, 386-393. (5) White, C. M.; Perry, M. B.; Schmidt, C. E.; Douglas, M. J. Energy Fuels 1987, 1 , 99. (6) Trytten, L. C.; Gray, M. R. Fuel 1990,69, 397.
0887-0624/92/2506-0068$03.00/0
and cyclopentanes, alkylbenzenes, alkylnaphthalenes, alkyltetralins, and several larger unsubstituted saturated, aromatic, and hydroaromatic ring compounds. Plots of the M W s of some of these hydrocarbons, calculated by eq 1-3, against their true MWs give slightly bent curves rather than the expected straight lines of slope = 1. The Winn equation and Trytten's version furthermore give a band of data points with somewhat different curves for different types of hydrocarbons. For instance, the PAHs (polycyclic aromatic hydrocarbons) fall either above or below the paraffins and alkylbenzenes. With White's equation the points fall into a narrow, though still slightly curved, band. Development and Testing of Our Correlations We found a version which seemed to have all the desired features of such a correlation: it gave a straight line for the plot of calculated versus true MW with a slope of 1, there was little spread between different types of hydrocarbons, and the calculated MWs were correct within an error of about A10 for the entire range covered by the model compounds (80-600). However, our correlation failed when we applied it to real oil samples. The calculated MWs were about 12% low, and data points lay on a curve which was still straight but tilted by this amount. Thus, to fit the oil data, we had to tilt the curve back up and then shift it down a bit, which led to our final equation (eq 4). Figure 1 demonstrates how well eq 5 fits the oil MW = 140 + 3.4
X
10-7(AEBP3/sp gr2.5)
(4)
data. but it also shows how far off these are from the 0 1992 American Chemical Society
Composition of Heavy Petroleums
Energy & Fuels, Vol. 6,No.1, 1992 69
Petroleum and Coal Oils 600
E,W .-
s m
-z 450 -i L 0
50350
2300
-5a 250 8 = 0
'%I
200
2b
300 350 400 450 500 550 600
Measured Molecular Weight Figure 1. Molecular weights of oil fractions calculated by Altgelt and Boduszynski's AEBP-sp gr equation vs true MWs: (+) 24 petroleum lube stock fractions;' (0)30 coal oil fractions;6 (-) n-paraffins, TRC data; (-) 45-deg line.
--
650 1
Table I. Original Range of MW and Sp Gr for the Four Correlations and Their Standard Deviations When Applied to Petroleum Lube Stock' and Coal Oil Fractions5 range correlation MW s p gr intcpt slope std dev R Winn, eq 1 80-6000 0.64-1.08 47 0.86 0.021 0.992 White e t al., 144-334 0.94-1.09 18 0.95 0.019 0.995 eq 2 Trytten and 190-349 0.85-0.99 -43 1.12 0.028 0.991 Gray, eq 3 Altgelt and 62-590 0.63-1.09 7 0.98 0.017 0.996 Boduszynski, eo 5 range correlation MW H/C intcpt slope std dev R Altgelt and 62-955 0.65-2.40 10 0.96 0.013 0.995 Boduszynski, eq 7 MW range on Winn's nomograph, not necessarily experimental.
Petroleum, Coal, and Syncrude Oils
I
,
600 550-
550-
5004501
350-
'585~
250
350
450
550
650
True Molecular Weight Figure 2. Molecular weights of n-alkanes (TRC data),calculated in four different ways, vs true MWs. Calculations by (1)Winn's original equation (I), (2) White et al. (-), (3) Trytten and Gray (o), and (4) Altgelt and Boduszynski (-). n-paraffins. The latter are still linear but appreciably steeper than the oil data. Equation 4 as well as two more given below use the Fahrenheit scale for the boiling points. We also need to point out that it is linear only for the range of heavy petroleum fractions, above AEBPs of about 500 O F (about MW 200). In the lower boiling range the curve bends up somewhat toward the low MW end. To make it linear for the entire range, we had to supplement them with the additional equation MW
