I
F. F.
PAPA-BLANC01 and MATTHEW VAN WINKLE
Department of Chemical Engineering, University of Texas, Austin 12, Tex.
Reduced Crude Oil-Dipropylene Glycol I iq uid- I iq uid Extraction System These data suggest how a solvent used in the petrochemical industry for purification of aromatics might behave if applied to heavy oils
THE
processing of reduced crude oil to produce materials meeting suitable specifications for sale or for further processing is of extreme importance. When reduced crude oils contain lubricating oil stocks in economic proportions, it is usual, through further treatment, to produce the lubricating oil stocks. When the reduced crude oil contains only small quantities of lubricants, it becomes necessary to consider the economics of further processing for the manufacture of salable or usable stocks which will realize the maximum financial return. Much of the reduced crude oil in this category can be used for catalytic cracking feed stock if the undesirable materials can be removed. A number of processes are used: high vacuum distillation, solvent deasphaltizing, and solvent extraction. In general, these processes are expensive, and new less expensive methods of treatment are constantly being sought. A number of solvents have been investigated, but most of them appear too costly for feed stock preparation. Because of the nature of some of the higher molecular weight glycols, it was considered possible that a solvent could be found which would have the necessary characteristics for economical processing of residual oils. In this study a dipropylene glycolreduced crude oil system was studied at 160' and 212' F.
Experimental Materials. Properties of the materials used are listed in Table I. Procedure. T o determine the phase boundary and phase equilibrium data, the following procedure was utilized. Measured amounts of reduced crude and solvent (dipropylene glycol) were placed in a separatory funnel. The mixture was shaken vigorously and then placed in a 1 Present address, ANCAP, Montevideo, Uruguay.
The heavier phase, extract layer, was drawn into a weighed separatory funnel and the raffrnate phase into a weighed centrifuge tube. The weight of the extract layer was determined, and the solvent was extracted by addition of measured amounts of distilled water. To facilitate separation and to reduce the tendency for emulsification, pentane was added to the mixture. The solventwater layer was removed and weighed,
constant temperature bath regulated within &l.O' F. of the working temperature. After 20 minutes the mixture reached the bath temperature and was removed from the bath and agitated thoroughly. It was then returned to the bath, where it remained from 5 to 24 hours, depending upon the relative amounts of solvent, until separation of the extract and raffinate layers was complete.
Table 1.
Properties of Materials Dipropylene Glycol
(Production) Specific gravity 20°/200 C. Specific gravity 60°/600F. 'API Viscosity S.S.U. at looo F. Viscosity-gravity constant Water content, % Distillation at 760 mm. Initial boiling point, O C. 50%, O C. End point, O C.
Reduced Crude (Mildly Vis-Broken)
...
1,0228
... ... ... ...
0.9254 21.4 313.7 0.877
...
0.1
...
226.3 231.1 236.5
Table II. Phase Equilibrium and Tie Line Data for Dipropylene Glycol-Reduced Crude Oil Vol. % Solvent VGC of Vol. % Solvent VGC of Solvent-Free in Raffinate Solvent-Freb in Extract Phase, SR Raffinate Phase, S E Extract 160' F.
4.8 5.0 5.7 5.6 6.6 9.0 9.9 12.0 13.1 4.2 4.2
0.875 0.871 0.868 0.867 0.860 0.854 0.849 0.843 0.841 0.881 0.888
9.1 9.2 9.5 10.1 10.9 13.4 15.9 19.7
0.875 0.872 0.870 0.867 0.862 0.856 0.847 0.845
212O
79.0 79.9 82.0 82.3 85.1 88.8 80.8 92.0 92.7 73.4 66.0
1.013 1.005 0.991 0.979 0.961 0.939 0.918 0.910 0.926 1.012 1.010
63.5 68.0 73.0 75.7 79.2 82.8 84.8 86.1
0.972 0.967 0.958 0.944 0.927 0.910 0.885 0.869
F.
VOL. 50, NO. 4
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100
90 80 70
+ Z
60
w
550
0 lJY
?? 40
30
20 IO
0 0.84 .85
.86
.87
.88
.89
.90 .91
VISCOSITY
Figure 1.
.92
- GRAVITY
.93
.94
.95
.96
.97
.98
.99 1.00
CONSTANT
Phase diagram for dipropylene glycol-reduced crude system ut 21 2' F.
IO0
90 80
70
I-
60
z W
30
50
lJY
8 40 30 20 IO
0 0.84
85
.86
.87
.88
.89
.90 .91
VISCOSITY
Figure 2.
704
-
.92 GRAVITY
.93
.94
.95
.96
.97
.98
CONSTANT
Phase diagram for dipropylene glycol-reduced crude system ut 160' F.
INDUSTRIAL AND ENGINEERING CHEMISTRY
.99
1.00 1.01
REDUCED CRUDE OIL-DIPROPYLENE GLYCOL and the procedure was repeated. The weight of solvent was calculated by difference. The amount of extract (pentane layer) was determined by weighing after the pentane had been evaporated by heating the pentane layer in a jacketed heater for 4 hours. The weight of the raffinate layer was determined, and the solvent contained in the raffinate layer was extracted with water in the same manner. Because the separation between the water-glycol phase and the oil (raffinate) phase was not sharp, it was found necessary to centrifuge the mixture. Upon centrifugation a brown material, apparently slightly lower in specific gravity than the water-solvent layer but suspended in this layer near the top, was observed. This material was insoluble in the oil layer and possibly was some form of asphaltene compound or mixture. The glycol-water layer was withdrawn with a pipet and the procedure repeated. The amount of solvent was then determined by weighing. The specific gravities of the solventfree raffinate and solvent-free extract were obtained by ASTM Method D 1217-52T ( I ) using pycnometers of 4.5ml. capacity. The kinematic viscosities were determined by ASTM Method D 445-53T (7). Kinematic viscosities were converted to Saybolt Universal viscosities by ASTM method D 446-53 (7). By determining the volume percentages, SR, solvent in raffinate phase, and SE,solvent in the extract phase, and the viscosity-gravity constants of both raffinate and extract, the equilibrium tie line and phase boundary data were obtained simultaneously.
1.0 2 1.0 I
1.0 0
.99 I-
2 k
X
w
VGC =
10G
- 1.0752 log ( V - 38) 10 - log ( V - 38)
where VGC = viscosity-gravity constant G = specific gravity, 6Oa/6Oo F. V = viscosity, Saybolt Universal seconds at 100' F.
.97
IA
0
.9 6
5
.93
LL
*
.92
k
.91
0 0
E
.90 8 9
.8 8 .8 7 0.8 6
.84 .85 VISCOSITY
-
-86 .87
.88
.89 .90
GRAVITY CONSTANT OF RAFFINATE
Figure 3. Equilibrium diagram for dipropylene glycol-reduced crude system
Discussion of Results The data resulting from the series of extractions a t 160' and 212' F. are reported in Table I1 and shown graphically in Figures 1 and 2. Because the reduced crude oil and its fractions represent complex mixtures whose actual contained compound composition is unknown, the conventional ternary composition diagram a t constant temperature cannot be used to present the data. Therefore some additive property must be used to indicate the degree of separation resulting from the addition of a solvent (5). The viscosity gravity constant (3) was used in this investigation. It is calculated by the following equation :
.9 8
a
Table 111. Equilibrium Data for Solvent Free Dipropylene Glycol-Reduced Crude Oil VGC at 160° F.
VGC at 212O F.
Raffinate
Extract
Raffinate
0.875
Extract
1.013
0.875
0.972
0.871
1.005
0.872
0.967
0.868
0.991
0.870
0.958
0.867
0.979
0.867
0.944
0.860
0.961
0.862
0.927
0.854
0.939
0.856
0.910
0.849
0.918
0.847
0.885
0.843
0.910
0.845
0.869
0.841
0.926
0.881
1.012
0.888
1.010
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VOL. 50, NO. 4
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APRIL 1956
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Figure 4. Bachrnan-type plot for dipropylene glycol-reduced
Figure 5 . Othmer-Tobias type plot for dipropylene glycol-reduced crude oil
crude oil The summation of possible errors in determining specific gravity and viscosity represented less than 0.05% in terms of viscosity-gravity constant. The possible errors resulting from the extraction procedure were estimated to be in the neighborhood of 2%. The phase diagrams with the tie line data shown in Figures 1 and 2, at 212'
and 160' F., respectively, indicate that the system is of a conventional type, with the two-phase area increasing with decreasing temperature. The equilibrium diagram shown in Figure 3 and Table I11 for both temperatures indicates the selectivity of the dipropylene glycol to be higher for the high viscosity-gravity constant ma-
Data for Bachrnan Plot of Dipropylene Glycol-Reduced Crude Oil 160' F. 212O F. Vol. % soln. Vol. soln. Vol. % raff. Vol. yo raff. in extr. phase, in extr. phase, in raff. phase, in raff. phase, R SE SE/R R SE SEIR Table IV.
95.2 95.0 94.3 94.4 93.4 91.0 90.1 88.0 86.9 95.8 95.8 87.4 a
79.0 79.9 82.0 82.3 85.1 88.8 90.8 92.0 92.7 73.4 66.6 94.2
0.831 0.841 0.870 0.871 0.910 0.975 0.998 1.043 1.064 0.768" 0.688" 1.076
90.9 90.8 90.5 89.9 89.1 86.6 84.1 80.3
63.5 68.0 73.0 75.7 79.2 82.2 85.3 86.1
0.699 0.750 0.807 0.841 0.891 0.950 1.014 1.070
Erroneous data.
Data for Othrner-Tobias Type Plot of Dipropylene Glycol-Reduced Crude Oil 160' F. 212O F. 1701. % ~ 7 0 1 . yo Vol. 7% Vol. % ' raff. s o h . in raff. in s o h . in - _... in raff. phase, (100 - extr. phase, (100 raff. phase, (100 - extr. phase, (100 S E )/ S E SE)/SE R)/R SE R SE R)l R R
Table V.
~
95.2 95.0 94.3 94.4 93.4 91.0 90.1 88.0 86.9 95.8 95.8 87.4
706
0.0504 0.0526 0.0604 0.0593 0.0707 0.0989 0.1097 0.1364 0.1507 0.0438 0,0438 0.1440
79.0 79.9 82.0 82.3 85.1 88.8 90.8 92.0 92.7 73.4 66.6 94.2
0.266 0.252 0.222 0.215 0.175 0.126 0.101 0.087 0.075 0.362 0.516 0.062
INDUSTRIAL AND ENGINEERING CHEMISTRY
90.9 90.8 90.5 89.9 89.1 86.6 84.1 80.3
0.1001 0.1013 0.1050 0.112 0.122 0.155 0.189 0.245
63.5 68.0 73.9 75.7 79.2 82.2 85.3 86.1
0.575 0.470 0.370 0.321 0.262 0.208 0.172 0.161
terial (asphaltic) at 160' than at 212' F. Consistency of the data was tested using the methods of Bachman (2) and Othmer-Tobias (6). The Bachmantype plot (Figure 4 and Table IV) correlates SEIR with ,S, where SE represents the volume per cent of solvent in the extract phase and R represents the volume per cent of raffinate in the raffinate phase. The Othmer-Tobias type plot (Figure 5 and Table V), relates (100 - R ) / R and (100 - S,)/S, on a log-log plot. Where the data are consistent through the entire range, the lines should be straight on both types of plots. In both cases curvature is evident at the upper end of the curves. This is not unusual in situations of this type, The data indicate that with a number of extraction stages the viscosity-gravity constant of the raffinate could be reduced to around 0.83. This is well within the range of viscosity-gravity constant for average lubricating oils ( 4 ) . However, some selective solvents are capable of reducing the value to 0.8, thus showing the selectivity of the glycol in the system investigated to be good but not better than some of the selective solvents now in use.
literature Cited (1) Am. SOC.Testing Materials, Philadelphia, Pa., Committee D-2, "ASTM Standards on Petroleum Products," 1953.
Bachman, I., IND.ENG.CHEM.,ANAL. ED. 12, 38 (1940). Hill, J. B., Coates, H. B., IND.ENG. CHEM.20, 641 (1928). Houghton, W. F., Robb, J. A., IND. ENG. CHEM.,ANAL. ED. 3, 144 (1931). (51 Hunter. T. G.. Nash. A. W., IND.ENG. CHEM.27, 836 (1935). ' (6) Othmer, D. F., Tobias, P. E., Zbid., 34, 693 (1942). RECEIVED for review April 6 , 1957 ACCEPTEDJuly 10, 1957 \
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