INDUSTRIAL
AND
ENGINEERING CHEMISTRY
A N A L Y T I C A L E D ITI 0N PUBLISHED
BY T H E
AMERICAN
CHEMICAL
SOCIETY
HARRISON
E.
HOWE,
EDITOR
Determining the Oil Content of Paraffin Waxes RUSSELL LEE AND V. A. KALICHEVSKY, Socony-Vacuum Oil Company, Incorporated, Paulsboro, N. J.
A
NUMBER of laboratory methods have been proposed
for the analysis of oil-wax mixtures (1-7, 10-14). Some of these methods were developed for use on waxy stocks containing large amounts of oil and are employed chiefly for controlling commercial dewaxing operations. These are not sufficiently accurate for the analysis of waxes containing small amounts of oil. Of the methods which have been proposed for the analysis of both scale and refined grades of paraffin wax, only the press method (2) has been used extensively in the petroleum industry. This is generally recognized to be lacking in accuracy and was abandoned as a tentative standard by the A. S. T. M. in 1939. The other published methods for the analysis of paraffin waxes involve complicated procedures or are limited in applicability to waxes of known origin. The analytical problem is complicated by the absence of a sharp line of demarcation between and "wax", owing to the existence of intermediate compounds which may be defined as either "oil" or "wax" (8, 9). An arbitrary definition of the boundary line between oil and wax is, thus, necessary in analytical methods of this type. This paper describes a simple and reliable method for the determination of oil in scale and refined paraffin waxes containing not over 10 per cent by weight of oil. The applicability of the method to waxes of higher oil content has not yet been fully investigated. The method is based on the selective separat,ion of oil and wax by solvent extraction
FIGURE2.
PRECOOLING
CH.4MBER
under carefully specified conditions. "Oil" is defined in this test as the percentage of solvent-free extract minus a correction of 0.15 per cent. The 0.15 per cent correction factor was developed empirically on waxes containing known quantities of oil and having melting points between 115O F. (46 O C.) and 145' F. (63' '2.). For waxes melting outside this range different factors may be necessary. The results obtained by this method are usually accurate to about * 0.05 per cent on oil-wax mixtures containing less than 1 per cent oil. The method involves dissolving a 25-gram sample of wax in 375 ml. of methyl ethyl ketone and chilling the mixture to -25' F. (-31.7' C.). A portion of the chilled mixture is filtered by means of an immersion-type filter leaf using vacuum. The amounts of oil and solvent in the filtrate are determined by evaporation of the ketone. As the proportion of solvent and oil in the filtrate is the same as that in the chilled mixture, the quantity of oil in the wax sample can be calculated by simple arithmetical rules. The filtration of only a portion of the chilled mixture eliminates the need of washing the wax cake with chilled solvent, thereby obviating errors due to occlusion of oil by the wax and permitting the use of relatively simple apparatus and procedure.
Apparatus The apparatus consists of the following items: Cooling vessels, V-shaped, of about 1-liter capacity and having the dimensions s h o m in Figure 1. Precooling chamber for filter leaf having the dimensions shown in Figure 2.
FIGURE1. COOLING VESSEL 767
768
INDUSTRIAL AND ENGINEERING CHEMISTRY
factory, provided its refractive index at 68" F. (20" C.) is 1.378 * 0.002 and the residue left on evaporating a 100-ml. sample by the procedure outlined below for evaporating solvent from the filtrate is not more than 0.002 gram.
I
I
Vol. 14, No. 10
Procedure A representative portion of the wax sample is melted in a suitable container, using a water bath or oven maintained at 160" F. (71" C.) to 180" F. (82; C.). The wax sample should not be held in the molten condition longer than is necessary for its complete liquefaction. Twenty-five grams ( * 1 gram) of the molten wax are weighed into a tared 500-ml. Erlenmeyer flask, making weighings to *0.2 gram, and 375 =t5 ml. of methyl ethyl ketone are added to the flask. A water-cooled condenser is attached to the flask and the mixture is heated on an electric hot plate or steam bath until the wax is completely dissolved, taking precautions to prevent surging of the solution into the condenser. The flask is then removed from the source of heat and, after boiling has ceased, the condenser is disconnected. The flask is then weighed to *0.5 gram and quickly stoppered with a cork equipped with a thermometer. The solution is allowed to cool to about 130" F. (54' C.) but before any wax precipitates it is poured into the V-shaped vessel in the cooling bath which is maintained at -35 * 5" F. (-37 rt: 3" C.), The wax solution is stirred with a thermometer at frequent intervals until the temperature reaches -20 F. (-29" C.) and then continuously until the temperature reaches -25 *0.5' F. (731.7 * 0.3" C.). The filter leaf is removed from the precooling chamber in the cooling bath and immersed quickly in the chilled mixture. The filter leaf is connected to a 250-ml. Erlenmeyer flask tared to *0.001 gram and to the vacuum system as shown in Figure 5. The vacuum should be maintained between 250 and 600 mm. of mercury gage. After about 100 ml. of filtrate have been collected in the flask, the suction is discontinued and the flask disO
-4 f" ,k F
W
FIGURE3. FILTER LEAF All parts nickel-plated
Filter leaves of the type shown in Figure 3. The filter medium is No. 8-0 filter canvas tightly fitted to the leaf. A qualitative grade of filter paper may be used on the circular leaf, provided it is supported by a perforated plate having a free area of not less than 40 per cent. Insulating cooling bath large enough to accommodate the desired number of cooling vessels and precooling chambers. The bath is filled with a suitable liquid such as methyl ethyl ketone which is refrigerated by solid carbon dioxide or brine circulation. The temperature of the bath is maintained at -35* 5" F. (-37 * 3" C.) throughout the test. Erlenmeyer flasks of 500-ml. capacity for preparation of the wax-solvent mixture. Erlenmeyer flasks of 250-ml. capacity for collecting the filtrate and evaporating the solvent therefrom. Lvaporation assembly as shown in Figure 4. Jets are provided for delivering a stream of clean, dry air vertically downward into the evaporation flasks. The inside diameter of the jet is 3 * 0.2 mm. and the tip of the jet is 25 * 5 mm. above the surface of the evaporating liquid at the start of evaporation. Air is supplied at the rate of 2 to 3 liters per minute per jet. The air is purified by passing it first through a commercial air filter and then through a 30-cm. column of 30- to 60-mesh fuller's earth. The cleanliness of the air is checked periodically by evaporating 100 ml. of methyl ethyl ketone in a water bath which is ma.intained at 95 * 2" F. (35 * 1 " C.). The residue left on evaporation should not exceed 0.002 gram. Thermometers of 0" to 300" F. range to measure the temperature of the wax-solvent solution and thermometers of -70" to +70° F. range to measure the temperatures of the cooling bath and cooling vessel.
Solvent Methyl ethyl ketone is used as the solvent in this test. The commercial grade is satis-
COMRCIAL AIR FILTER
W I F O L D I8 JETS SHOWN1
___--_-_____--__
!
_1
FIGURE 4. EVAPORATION ASSEMBLY
--
OF KNOWN OIL-WAX MIXTURESBY PROPOSED METHOD TABLE I. ANALYSIS
Oil Component Wax Component
w -
No.
Description
Melting point O
1 2 3 4 5 5 5 5 5 6
Deoiled refined wax
Refined wax
6 6
7 7 7 0
Pensky-hfartens.
F.
132.2 131.4 124.0 123.2 123.7 123.7 123.7 123.7 123.7 131.1 131.1 131.1 123.2 123.2 123.2
Pour point O
F.
9.u. v. at
100' F.
.. .. ....
...
15 15 15 15
94.3 94.3 94.3 94.3
0 15
90.7 86.8
15 20
86.8 196.0
.. .. ..
... ... ...
...
... ...
Flash point F."
...
... ... ... ...
320 320 320 320
... ... ...
...
...
...
Oil Content
%by wt. of blend 0.00 0.00
0.00
0.00 0.00 0.19 0.38 0.99 2.09 0.00 0.49 0.41 0.00 3.84 0.99
Foundby proposed Caloumethod lated % bu wt. 0.00 0.00 0.00 0.05 0.00
0.08
0.18 0.34 0.89 1.72 0.19 0.75
0.56 0.41 4.03 1.39
0.00 0.00 0.00 0.00 0.19 0.38 0.99 2.09
0:68 0.60 4:25 1.40
ANALYTICAL EDITION
October 15, 1942
169
Results
-
The accuracy of the results obtained in determining the oil content of paraffin waxes by the described method is illustrated by Table I. These results were obtained on deoiled refined waxes and known blends of dewaxed oils with refined waxes before and after deoiling. For waxes containing less than 1 per cent oil, the method gives results which are usually accurate to *0.05 per cent. The interlaboratory reproducibility of the method is demonstrated by the data in Table 11. Except in one instance, the results from different laboratories differ from the average by less than 0.1 per cent. A comparison of results obtained by the proposed method and the press method is shown by Table 111. These data show that scale and refined paraffin waxes can be readily differentiated on the basis of oil contents as determined by the proposed method but not by the press method.
I
FIGURE5 .
FILTR.4TION
ASSEMBLY
connected from the filter leaf and vacuum system. The outside of the flask is washed with acetone, wiped off with a cloth, and weighed to *0.2 gram. The methyl ethyl ketone is evaporated from the filtrate, using the evaporation assembly described above. The flask is weighed t o +0.001 gram after 2 hours' evaporation and then after 0.5hour evaporation periods until the loss between successive weighings is not over 0.002 gram. The flask should be rinsed with acetone to remove water, placed on a paper towel or other blotter to dry for one minute, then placed in a desiccator containing anhydrous calcium chloride a t balance room temperature for about 15 minutes prior to weighing. The time required for evaporation is usually 2.5 hours. The oil content of the wax sample is computed by the following equation: (weight of oil in filtrate) X (weight of solvent in charge . mixture) - 0.15 (weight of wax sample) X (weight of solvent in filtrate)
Oil, yoby wt,. = loo
TABLE 111.
COMPARISON OF PRESS AND PROPOSED
METHODS
Oil Content
Wax Sample
a
Press methoda (Duretta cloth)
Refined wax 119.6' F.m . p . 123.6' F.m. p. 126.4" F. m. p. 131.0' F.m. p . Scale wax 118.8' F. m. p . 123.0' F. m. p . 126.4' F. m. p . 128.2' F. m. p . A. S. T. 11.D-308-29T (abandoned in
Proposed method
70 b y weight 1.2 1.3 1.0 1.4
0.45 0.35 0.27 0.15
2.3 0.8 1.0 1.1 1939).
3.78 2.98 0.89 0.52
Acknowledgment
In performing this test, special care should be exercised to keep the equipment clean. This applies particularly to the filter leaf. The cleanliness of the filter leaf can be checked by filtering through it about 100 ml. of methyl ethyl ketone at ordinary temperatures and evaporating the filtrate as previously outlined. The residue should not exceed 0.002 gram.
The authors wish t o express their appreciation to J. B. Rather for permission to publish this article, and to thank L. C. Drake, T. A. Petry, T. G. Roehner, and E. L. Smith of the Socony-Vacuum Oil Co., Inc., and E. L. Ruh and A. Williams of the Standard Oil Co. of Yew Jersey for many helpful suggestions in t h e development of this method.
REPRODUCIBILITY O F PROPOSED METHOD
Am. SOC.Testing Materials, Proc., 27, Part I , 450-4 (1927); 28, Part I, 445-9 (1928).
Literature Cited TABLE
11.
INTERLABORATORY
Oil Content
7
Laboratory A
Wax Sample 130-132' F. m. p . , refined wax
Av. 128-130' F. m. p , , refined wax
0.17 0.17 0.17
0.29 0.25 Av. 0 . 2 7 126-128" F. m. p . , 0.30 refined wax 0.28 Av. 0 . 2 9 122-124' F. m. p . , 0.34 refined wax 0.36 Av. 0 . 3 5 126-128' F. m. p . , 0.95 scale w a x 0.91 Av. 0 . 9 3 121-123' F . m. p . , 1.83 scale wax 1.85 Av. 1 . 8 4
~Naximum Average Deviation Labora- Labora- of three from tory B tory C laboratories Average Per cent b y weight
0.19 0.21 0.20 0.24 0.22 0.23 0.35 0.38 0.37 0.41 0.41 0.41 0.89
0.90 0.90 1.72 1.76 1.74
0.18 0.11 0.15 0.17 0.24 0.21 0.40 0.40 0 40 0.47 0 39 0.43 1.25 1.15 1.20 1.83 1.89 1.86
0.17
0.03
0.24
0.03
0.35
0.06
0.40
0.05
1.01
0.19
1.81
0.07
Ibid., 29, Part I, 359-61, 682-6 (1929). Burch, E. A., Refiner, 17, No. 11, 598-602 (1938). Diggs, S. H., and Buchler, C. C., IND. ENQ.CIIEM.,19, 125-7 (1927). Hall, F. W., and McCarty, B. Y., Nutl. Petroleum News, 29, NO. 28, R-15-25 (1937). Holde, D. (Mueller, Ed.), "Examination of Hydrocarbon Oils and Saponifiable Fats and Waxes", 2nd ed, pp. 108, 110, New York, John Wiley & Sons, 1922. Horne, 3. W., and Holliman, W. C., Bur. Mines, Tech. Paper 583 (1938). Kalichevsky, V. A . , "Modern Methods of Refining Petroleum Oils", pp. 30-2, New York, Reinhold Publishing Corp., 1938. Kalichevsky, V. A., and Lee, R., J. Inst. Petroleum Tech., 24, 59-60 (1938). McKitterick, D. S., Henriques, H. J., and Wolfe, H. I., Ibid., 23, 616-41 (1937). Schwartz, F., and Huber, H. von, Chem. Rev. Fett u. Haw I d . , 20, 242-4 (1913). Weld, D. P., and Rather, J. B., Refiner, 8, 102, 106, 110, 114 (1929). Wilson, R. E., and Wilken, R. E., IND.ENQ.CHEM.,16, 9-12 (1924). Wyant, L. D., and Marsh, L. G., Bur. Mines, Tech. Paper 368 (1925).
