INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1955
NOMENCLATURE
D, Do D
= =
b
1 = - =
density of solvent density of oil = density of mixture AD = calculated density of mixture minus observed density 1 = - = specific volume of solvent a D, specific volume of oil
D O
z
=
weight fraction of oil in mixture
v
=
1 = specific volume of mixture D
v, = calculated
specific volume
Of
1049
AV = Vt - V = AV when x = 0.5
k
LITERATURE CITED
(1) Dunken, H., 2. physik. Chem., 53B,264-79 (1943). (2) Magne, F. C., Durr, R. L., and Skau, E. L., J . Am. Oil Chemists' SOC., 30,8-9 (1953). (3) Magne, F. C., Hughes, E. J., and Skau, E. L., Ibid., 27, 552-6 (1950). (4) Magne, F. C., and Skau, E. L., IND.ENG.CHEM.,37, 1097-101 (1945). (5) Natl. Bur. Standards, Circ. C 410 (1936). EECEIVED for review August 2, 1954.
mixture, assuming ideal
solutions
ACCEPTED Sovember 26, 1954. The mention of firm names and trade products does not imply t h a t they are endorsed or recommended by the Department of Agriculture over other firms or similar products not mentioned.
Empirical Viscosity Relations of Heated Vegetable Oils R. P. A. SIiyPS Division of Chemistry, Science Service, Department of Agriculture, Ottawa, Canada
A
LTHOUGH a precise relation between bulk viscosity and polymer content of bodied vegetable oils has not yet been established, viscosity is generally used as an index of polymerization. The analogy between polycondensation reactions and thermal polymerization of drying oils has been recognized for some time. Nevertheless, the statistical approach t o an explanation of the analogy has been made unrewarding by the complexity of the reaction and the incomplete knowledge of the distribution of the functional groups in the starting material ( 1 ) . More recently, the bulk viscosity of tung and oiticica oils has been re-
0.9550
i
0'g350r P /
0.9300
0'9250
PP,
0.920ot-J
0
1
,
,
I
2
.
3
, 4
, 5
6
, 7
T I M E , HRS.
Figure 1. Relation between density of a bodied oil and polymerization time 0 Linseed oil, 310' C.
0 Tung oil, 1 9 5 O C. A Safflower oil, 320' C.
lated to rate equations for their thermal polymerization ( d ) . However,' the relations were based on viscosity equations that apply only to dilute solutions. Xevertheless, certain published data ( 3 , 6) suggest a possible relation between the viscosity and polymer content of linseed oil. Therefore, to determine whether a useful empirical relation exists, the properties of polymerized linseed, safflower, and tung oils were investigated. MATERIALS AND METHODS
Linseed, safflower, and tung oils were used in this study. The linseed and safflower oils were alkali-refined and bleached before use; the tung oil was polymerized without preliminary purification. The apparatus employed and conditions of polymerization have been described (7'). Part of each sample of oil was saponified by refluxing a mixture of 5 grams of oil, 2 grams of potassium hydroxide, 5 ml. of water, 10 ml. of benzene, and 5 ml. of methanol for 4 hours. Methyl esters were formed b y the action of diazomethans in anhydrous ether on the fatty acids obtained from the saponified samples. Resaponification of the methyl esters and their reformation did not change the amount of trimeric and n-meric material in the sample as determined by molecular distillation. The amount of polymeric glyceride and ester in the samples was determined with a micromolecular still (8). The still consists of a shallow glass pan suspended from a sensitive quartz helix in the longitudinal axis of a tube containing an internal heating coil and thermocouple. With a pressure of 1 0 - 6 mm. of mercury, the following relation obtained between molecular weight of distilland and temperature of maximum rate of evaporation, 300:90" C., 600:180° C., 900:270" C. Some samples of linseed and tung oil and their methyl esters mere hydrogenated prior to molecular distillation. The hydrogenation apparatus was a modification of that described by Pack and coworkers el al. ( 4 ) . The platinum on silica catalyst was prepared according to Vandenheuvel (9) and cyclohexane wai used as the solvent. Extraction of the catalyst with ether in a Soxhlet-type extractor for 3 hours resulted in complete recovery of the reduced oil or ester. The oils and esters were hydrogenated to an iodine value of less than 10. With 0-hour samples, the reduced material had the melting point of the corresponding stearate.
Vol. 47, No. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
1050
100.0
Table I.
Effect of Hydrogenation on Amount of Distillable Material in Heated Oils and Their Esters Linseed Oils,
Heating Time,
320' C. Before After Hz H2
Hr. 1.0 2.2 6.0 1.0 2.2 6.0 1.0 2.2
Polymeric glycerides Dimeric acyl groups Trimeric acyl groups
65:40
. .,
23:kI
...
22:io
1o:iz
ii:So
...
... ... 2.53 ...
6.0 1.0
n-Meric acyl groups
63:73
...
2.2 6.0
Tung Oil, 195' C. Before After Hz H2 85
25.17
loo
6s 35
...
:
9.93
10.11
33.08 1.03
33:$7 0.96
2.92 0.63
3.51 0.29
1.46
2178
...
...
...
... ...
...
2.95
40.0
vl
10.0
W
e f-
4.0
vl 0
'" >
1.0
0.4
0 J
0
I 10
I I I I 20 30 40 50 Yo POLYMERIC GLYCERIDES
I 60
I 70
Figure 3. Relation between kinematic viscosity and per cent polymeric glycerides
I 1
0
I
I
I
2 TIME,
I
3
I
4
1
5
I
6
HRS.
Figure 2. Semilogarithmic relation between viscosity and polymerization time
Density of the samples was determined by the falling drop method (6) or by calibrated pycnometer. Viscosity was measured in Ostwald-Fenske pipets. During density and viscosity determinations, temperature was controlled to =l=0.02QC. One sample of linseed oil was stripped of its nonglyceride components on a centrifugal molecular still (Type CMS-5, Distillation Products, Inc., Rochester, K. Y.). The oil was cycled 10 times a t 90' C. while the Pirani gage indicated 0 micron of mercury.
the rate of density increase fell off slowly and continuously after a short, initial, linear period. When the logarithms of kinematic and dynamic viscosity were plotted against polymerization time, straight lines were obtained over much of the range (Figure 2 ) . With linseed oil, this linear relation applied up to a viscosity of approximately 4.0 stokes; with tung oil, up to 34 stokes; and with safflower oil, between 0.9 and 20 stokes. The parallel curves obtained (Figure 2 ) for kinematic and dynamic viscosity indicate that, for following the progress of thermal polymerization, kinematic viscosity is as useful an index as dynamic viscosity. Kinematic Viscosity-Polymer Content Relations. Because rate of thermal polymerization is appreciable a t the highest temperatures used in molecular distillation, the possibility that polymer content might be increased during distillation was investigated. Samples of nonconjugated and conjugated oils were therefore distilled before and after hydrogenation. The results
Table 11. Comparison of Linseed Oil Heated in Sealed Tubes and Swept Reactor
Conditions 220" C . , sealed tube 310' C., Na sweep
EXPERIMENTAL AND RESULTS
Kinematic-Dynamic Viscosity Relations. As kinematic viscosity was measured in this investigation, density measurements were also required for calculation of dynamic viscosity. The relation between density and heating time was therefore investigated for the different oils (Figure 1). The results for linseed and safflower oils suggest a linear gain in density with heating times of 2 and 4 hours, respectively. With longer heating times,
31OOC sealed
tubes'
Heating Time, Hr.
P
30,
Stokes
Polymeric Glyoeride,
%
384
2.197
44.16
0.06 0.40 0.76 1.13 1.49 1.81 2.52
0.400 0.587 0.852 1.249 1.815 2.541 4.872
1.00 12.16 22.27 32.13 39.74 45.93 56.70
Volatile Components
% ' Distillabl;! at
90" C. 0.62
180° C. 3.07
0.48
3.66
i:ii .. i:ie
2:99
..
1.38 0.47
3:08 3.32 2.95
1:77
4:74
2:39
..
5: 05
2:95
3:95
..
..
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1955
1051
A , LINSEED 100.0 7
100.0-
40.0 -
40.0
f 10 0
-
-
7'. 4.0
40-
IO
-
-
-
1.0-
0.4 -
04
-
67
w Y 0
c fn
I
I
1
0
10
20
I 30
I
I
I
I
I
1
I
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40
100.0-
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0-
0 0 fn
> 400-
40-
100-
10-
4.0
10
-
0.4
1
1
I
I
10
20
30
a0
O1
-
'
0
I
1
I
10
20
30
in their viscosity-polymeric glyceride relation (Figure 3). Tung oil contained the least and safflower oil the most polymer for a given viscosity. During the same period that safflower oil polymerized a t a slower rate than linseed oil, it had less polymer than linseed oil. With the micromolecular still used in this investigation, it was possible to separate esters from polymerized oils into monomer, dimer, trimer, and n-mer, where n is greater than 3. Therefore, log v can be related to the concentration of these esters and to their sum, designated here as "polymeric" acyl groups. The data obtained a t 310' and 220' C. with linseed oil and a t 320' C. with safflower oil were very much alike (Figure 4). Formation of dimeric acyl groups appeared to be the major reaction. However, as rate of dimer formation fell off, the concentration of trimeric and n-meric
trimer and n-mer was but a small part of the bodying of a conjugated oil. Although linseed oil heated a t 220' C. had the same dimeric and polymeric content as linseed oil heated at 310" C., formation of trimeric and n-meric groups appeared slower a t the lower temperature. The ratios of timer to dimer linseed and safflower oil increased with increasing viscosity (Figure 5 ) . With oils heated a t high temperatures, the rate of increase became less after a viscosity of about 6 stokes was reached. At 220' C., the rate of change decreased continuously. Concurrently, the ratios of n-mer to dimer and n-mer to trimer increased, making the ratio of polymer to dimer increase almost linearly with log viscosity. With tung oil, the ratios remained small and relatively constant, except for the ratio of n-mer to trimer, which increased rapidly until a viscosity of about 6 stokes was reached.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1052
40.0
c
6 . SAFFLOWER
A. LINSEED lO0.Oj-
t
I 10
1
0.1
I
0.2
I
I 0.4
0.3
I
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1
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0.5
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0.2
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,
0.8
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t u) D. LINSEED
0 0
'" >
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220°C.
IO.
