Simulated Distillation of High Boiling Petroleum Fractions
SIR: Simulated distillation, a gas chromatographic method for obtaining boiling point distribution, has been applied to petroleum distillates with end points u p to 1000’ F. ( I ) . Now the method has been extended to crude oils, highly aromatic “decanted” oils, and other full range petroleum fractions with end points above 1000’ F. Materials with an initial boiling point above 350” F. require only a single analysis with internal standard. Crude oils or other full boiling range materials (-44’ F. to > 1000’ F.) require two analyses, one with and one without internal standard.
EN^
;TART I
EXPERIMENTAL
Figure 1 .
The simulated distillation equipment is the same as described previously ( I ) , except that 15-inch columns packed with 0.5% SE-30 on Chromosorb G are used. Method 1. If the sample has a n initial boiling point above 350’ F., approximately lOyo by weight of n-octane is added as internal standard. Solid or highly viscous samples are further solubilized with a low boiling solvent such as benzene. T h e mixture is analyzed as previously described (1). The per cent boiling below 1000’ F. is found by comparing the ratio of internal standard area counts to the known per cent of internal standard. The equation for the calculation is : 100
x
wt. internal std.
wt. sample
B.
Illustrative chromatograms
Sample plus Internal standard Sample only
Chromatograms of the type obtained by method 2 are shown in Figure 1. Referring to this figure, the following points should be discussed. If the weights of sample in the two runs are equal, the area relationships are ( t b to) = (to’ - t o ’ ) and (Z - t u ) = (Z’tu’). The areas (tu - t b ) and (tu’ - tb’) differ by the area due to the weight of internal standard. However, the samples in the two runs are seldom equal. The ratio of the (Z - t,) and (2’ - tu’) areas is used to adjust the (tu‘ - to’) area so that the area due only to the internal standard can be established. Then the per cent boiling below 1000’ F. is equal to:
X
area counts sample Area counts internal std.
(Z
-
% boiling below 1000’ F. Method 2. If t h e sample has a n initial boiling point below 350’ F., there is no vacant area of t h e chromatogram where a n internal standard can be eluted free from interference of sample or solvent components. This fact is particularly true in t h e case of full boiling range samples such as crude oils. Analysis of these samples is accomplished by two runs, one with and the other without internal standard. The first run is made on the sample as received, and the second on the sample with 20% by weight of internal standard added. By using a mixtuce of n-paraffinsnonane through dodecane as internal standard, an area on the chromatogram due to internal standard can be obtained which is more equivalent to that due to sample in the same boiling range, and yet the total detector response remains linear. 1620
A.
ANALYTICAL CHEMISTRY
- to)
- t 5 ) - [(Z- t a l x (ta’ - t 5 ’ ) / ( 2 ’ - t a ’ ) l
-1
(to
1
100
Where S = wt. internal std./wt. sample and ( 2 , tu, t b , to) and (z’, tu’, tb’, to’) refer to the designated points on Figure 1. The boiling point distribution is calculated on the sample run without internal standard.
Distillation curves of Wilmington and Wasson crude oils, obtained by the V. S. Bureau of Mines, Bartlesville, Okla. (S), and by our laboratory are compared to simulated distillation results in Figures 2 and 3. These two crudes represent widely different types. Generally all the curves are in good agreement. TheT.B.P.curvesappear to show a false temperature rise immediately after the column pressure is reduced. This temperature rire occurs at approximately 450’ F. in the case of the American Oil T.B.P. curves and 575’ F. on the Bureau of hIines curves. Improper temperature conversion is a n unlikely cause, because conversions were calculated independently and from different observed pressures. The more likely explanation is the time required to reach actual equilibrium a t the reduced pressure and/or losses during evacuation of the column. The T.B.P. curves gradually approach the S.D. curve again after operation at reduced pressure, and a sniooth curve drawn between the atmospheric section of the T.B.P. curves and the final points under reduced pres-
RESULTS AND DISCUSSION
True boilingpoint (T.B.P.) distillations of two crude oils, two heavy gas oils, and a “decanted” oil were made on 100 theoretical plate spinning band columns. When the overhead temperature reached 400’ F., the column pressure was reduced to 1 mm. Hg. Data points were observed at 1% fractions. The fractions were weighed and the losses were prorated over the entire boiling range. These data were compared to those obtained by the simulated distillation (S.D.) method on the samples.
Table 1.
Comparison of Calculation Procedures Xt. 70 off at 1000” F. Crude hlethod 2 hlethod la 66.3 64.2 Wilmington Wasson 91.5 88.2 89.4 90.8 Drumright C7 and lighter analysis ( 9 ) used internal standard-single S.D. Run.
as
I200
I
I
I
I
I
I
I
I
I
I
I-
0
0
I
I
I
I
1
I
I
1
I
10
10
30
40
SO
60
70
10
90
10
IO0
20
30
Figure 2.
Figure 3.
Wasson crude oil
sure closely follows the S.D. curve. The dotted portion of the S.D. curve is an extrapolation of the data to llOOo F. As a further check on the accuracy of simulated distillation method 2, the area on the S.D. chromatogram due to C7 and lighter components was set equal
7c
Off
IBP 10 20 30 40 50 60 70 80 90 95 100
Virgin gas oil T.B.P. S.D. 446 517 580 622 650 693 742 783 836
...
... ...
419 506 562 610 659 704 749 795 844 910 951 1009
60
70
10
90
100
to the % C, and lighter, determined by the method of Martin and Winters ( 2 ) . This area was used to calculate the per cent boiling below 1000° F., and the values obtained for three crude oils are compared with those determined by method 2, in Table I.
Distillation of Heavy Gas Oils
Temperature, O F . High sulfur coker gas oil T.B.P. S.D. 433 526 565 600 636 672 710 751 800 863 900
...
Wilmington crude oil
Oil R&D T.B.P. 0 Bureau of Mines T.B.P.
Oil R&D T.B.P. 0 Bureau of Mines T.B.P.
Wt.
‘10
0 American
0 American
Table II.
40
W T I DISTILLED
W T % DISTILLED
409 498 544 593 651 688 727 770 814 872 922 1007
Comparisons between T.B.P. distillation and S.D. values for two heavy gas oils and a decanted oil are shown in Table 11. The S.D. values were obtained by method 1 using n-octane internal standard. Again the agreement is good. The decanted oil is of particular interest because it contains a high percentage of polycyclic aromatic compounds. LITERATURE CITED
“Decanted” oil T.B.P. S.D. 374 605 645 675 710 734 770 797 833
... ... ...
348 575 640 676 707 736 768 797 830 876 918 1007
(1) Green, L. E., Schmauch, L. J., Worman, J. C., ANAL.CHEM.36, 1512 (1964). ( 2 ) Martin, R. L., Winters, J. C., Ibid., 35, 1930 (1963). (3) Smith, H. &I., U . S. Bur. Mines, Rept. Invest. No. 6542 (1964).
J. C. WORMAN L. E. GREEN
Research and Development Department American Oil Co. Whiting, Ind.
VOL. 37, NO. 12, NOVEMBER 1965
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