Composition of High-Solvency Hydrocarbon Thinners E. H. MCARDLE, J. C. MOORE, H. D. TERRELL, E. C. HAINES, AND COOPERATORS1 Philadelphia Paint and Varnish Production Club, Philadelphia, Penna.
recting for the dissolved sulfur dioxide in the acid raffinate, the aromatic fraction, X, is found according to the equation
Data gathered by ten laboratories, working in six cooperating groups, show that a recent method of estimating the aromatics, naphthenes, and paraffins in substantially olefin-free hydrocarbon thinners of the high-solvency type provides adequate precision and accuracy in the determination of aromatics. Naphthenes and paraffins are found less accurately, but aromaticity is apparently the important property. Accuracy and precision were checked by analyzing commercial thinners, blending pure hydrocarbons according to these results, and analyzing the blends; and by comparing viscosities of resin solutions in each pair of thinners. As it stands, the method is not recommended for the proximate analysis of lowsolvency thinners
1.4950 - X
+ refractive index of raffinate refractive (1 - X) = index of thinner
Naphthenic and paraffinic contents of the nonaromatic fraction are read from one of a family of curves corresponding to the boiling range of the thinner in question (6, 7). One means of checking the accuracy of the method is to compare the determined composition and solvency of commercial thinners with those of corresponding synthetic blends of pure aromatics, naphthenes, and paraffins of the same boiling ranges. Accordingly, the present cooperators have analyzed three commercial petroleum naphthas whose evaporation rates are just faster than toluene-thinners C, D, and F-and also synthetic blends made from toluene, 98 per cent pure methylcyclohexane, and pure n-heptane, according to the median results obtained for these naphthas by the cooperating laboratories in last year’s work (6). Percentages of aromatics, by volume (3, 6),were found in the usual manner. Naphthenes and paraffins, however, were determined in the nonaromatic fraction from a nomograph (Figure 1) adapted from the family of curves previously referred to (6, ?‘), but differing in that the “average boiling point”, instead of the boiling range, of the thinner is used. It is felt that the average of the 10, 20, 30, 70, 80, and 90 per cent points of an A. S. T. M. distillation more closely defines the average molecular weight of a thinner and hence the refractive indices of the major naphthenic and paraffinic components, than does the boiling range-i. e., the spread from A. S. T. M. initial to A. S. T. M. final boiling point. Average boiling point has been found to correspond closely to both the 50 per cent point and the so-called “weighted average.”
.
I
N 1938 the Philadelphia Paint and Varnish Production
Club developed a rapid method for the proximate analysis of hydrocarbon thinners derived from petroleum and coal tar (6). To check the precision of the method, several cooperating laboratories obtained results showing satisfactory agreement when analyzing six commercial thinners, of the usual boiling ranges, whose aromatic contents exceeded 35 per cent. Low-solvency naphthas, however, of the lacquer diluent (varnish maker’s and painter’s naphtha) and “mineral spirits” types did not lend themselves to good precision of analysis, and hence work is now in progress to refine the procedure. Accuracy of the method was tested by only one cooperator. Further, it was felt that a family of curves which were used to determine naphthenic and paraffinic content permitted too great an error in selection and reading. Hence, to provide greater accuracy, as well as to prove the utility of the method for evaluating the higher solvency naphthas, the present cooperative work was undertaken. As it stands, the proximate analytical method requires the removal of aromatic hydrocarbons present in the usual commercial thinners by whirling rapidly, in a 125-cc. glassstoppered Erlenmeyer flask, 10 cc. of thinner with 20 cc. of c. P. 20 to 30 per cent sulfur trioxide fuming sulfuric acid. A good emulsion should be obtained. During the first 5 minutes of contact the flask should be cooled by immersion in ice water. A second 5 minutes of rapid whirling in the air, with the stopper set loosely, is followed by 30 minutes of settling, decantation of a few drops of raffinate (now saturated with sulfur dioxide), and the determination of the refractive indices a t 20” C. of both raffinate and original thinner. Assuming (6) the average refractive index of the aromatics present in substantially olefin-free commercial thinners boiling above 95” C. and below 200” C. to be 1.49g0, and cor-
TABLEI. ANALYSISOF THINNERS Aromatics (volume per cent of toluene) Naphthenes (volume per cent of methylcyclohexane) Paraffins (volume per cent of n-heptane)
C
D
F
%
%
%
38.0 S 8 67.7 33.5 15.9 17.8 2 8 . 5 7 5 . 3 14 5
OF HIGH-SOLVENCY NAPHTHAS TABLE11. COMPOSITION
(Cooperators 1 t o 6)
Thinner
1
Commercial C Synthetic C Commercial D Synthetic D Commercial F Synthetic F
38.2 37.7 8.2 9.0 69.4 67.6
Commeroial C Synthetic,C Commercial D Synthetic D Commercial F Svnthetic F .“
34.5 28.2 21.1 9.1 17.7 12.9
Commercial C Synthetic C Commercial D Synthetic D Commercial F Synthetic F
27.3 34.1 70.7 82.0 13.0 19.5
2
3
4
Av.
Av. Deviation
38.1 38.0 8.8 9.1 68.9 66.9
0.43 0.47 0.92 0.33 0.48 0.62
33.7 33.9 34.3 27.2 24.0 27.7 18.2 14.0 18.2 7.5 8.3 9.3 18.6 18.7 18.1 13.8 17.4 14.7
0.7 1.7 2.4 1.3 0.4 1.3
6
5
Per Cent Aromatics by Volume 38.5 3 8 . 0 37.2 38.2 8.4 8.2 8.8 9.1 67.8 69.6 66.7 6 7 . 4
37.0 37.6 9.2 8.4 68.6 66.4
38.4 38.1 8.6 9.5 69.0 67.5
38.7 39.0 10.3 9.6 68.7 65.7
Per Cent Naphthenes by Volume 34.9 31.4 19.6 11.0 18.2 15.9
35.3 33.4 28.4 26.8 2 1 . 3 15.0 11.5 8.2 17.6 17.9 13.8 14.5
Per Cent Paraffin by Volume
Committee: A. H. Stover, G . R. Henry, K. G. 1 E. C. Haines, chairman. Krech, J. Binswanger, J. B. Hill, and E. S. Esposito.
248
26.6 31.4 72.0 80.2 14.0 17.4
26.7 33.4 70.5 79.5 12.8 18.8
29.6 35.6 75.8 83.4 13.5 19.1
27.9 34.7 72.2 83.0 12.4 18.7
27.4 37.0 74.8 82.0 11.6 16.9
27.6 34.4 72.7 81.7 12.9 18.4
0.8 1.4 1.8 1.2 0.6 0.8
ANALYTICAL EDITION
MAY 15, 1939
TABLE111. REFRACTIVE INDICES AT 20" C. (Figure a t the left of decimal omitted) 4434 4440 4434 4436 Commercial C 4437 4398 4392 4392 4397 Synthetic C 4391 4082 4080 4078 4077 Commercial D 4084 4026 4020 4018 4022 Synthetic D 4023 4699 4696 4683 4695 Commercial F 4695 4659 4658 4658 4660 Synthetic F 4652 Refractive Indices c)f Raffinate a t 20' C. 4121 4115 4121 4112 Commercial C 4113 4070 4057 4053 4049 Synthetic C 4034 3997 4004 4000 3998 Commercial D 3984 3933 3925 3932 3925 3920 Synthetic D 4121 4120 4124 4128 Commercial F 4134 4074 4056 4048 4056 Synthetic F 4082 Average Boiling Point Commercial C Synthetic C Commercial D Synthetic D
O C./" F. 110.5/231 101.5/215 108.3/227 98.9/210
4422 4387 4068 4008 4689 4650 4112 4048 3979 3922 4121 4058 O
Commercial F Synthetic F
Table I1 shows that the present cooperators concord reasonably well in the compositions of the two commercial high-solvency type naphthas, as well as in the compositions of their synthetic matches. Accuracy of the method, as it stands, is of the order of ~ 0 . 5 per cent of the whole thinner in the aromaticity of the two commercial high-solvency naphthas; and aromaticity is considered the most important property of a high-solvency thinner. Baldeschwieler et al. (1, 2) have shown that, according to kauri-butanol values, an aromatic hydrocarbon, in the usual commercial boiling ranges, has approximately double the solvency of the corresponding naphthene, which in turn has nearly double the solvency of the paraffin. On the other hand, both accuracy and precision are poor in the case of the single lowsolvency naphtha, and work is now in progress to refine the method to deal with such materials. These results in Table I1 are derived from the refractive indices and average boiling points given in Table 111. Considering the two high-solvency type naphthas C and F, whose aromaticities agree reasonably well with those of their corresponding synthetic matches, poor agreement is observed between the paraffinic and naphthenic contents of the commercial products and their synthetic matches. It is probable that a part of the discrepancy is due to the wide difference in the types of paraffins present: mixtures of highly branched paraffins
e./' F .
110.5/231 105.5/222
249
in the high-solvency commercial naphthas us. n-heptane alone in the synthetic blends. A further estimate of the accuracy of the proximate analytical method, as it stands, is a comparison of the viscosities of solutions in each pair of commercial and synthetic thinners of resins and a standard nitrocellulose solution. I n addition, the comparative kauri-butanol values, mixed aniline points, and refractive indices serve as accuracy indications. Table IV lists these various comparisons. Each cooperator used the same alkyd resin, modified phenolic and 37.5 per cent solution of 0.5-second nitrocellulose (containing 20 per cent ethanol) in n-butyl acetate. Kauri-butanol solutions, however, were of dissimilar strengths; and two cooperators substituted the mixed aniline point test for the kauri-butanol determination. Mixed aniline point is the critical solution temperature of a mixture of 5 cc. of thinner, 5 cc. of any
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FIGURE1. COMPOSITION-BOILING POINT-REFRACTIVE INDEX CHART FOR AROMATIC-FREE NAPHTHA
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
250
TABLEIV. COMPARATIVE VISCOSITIES~ Thinner Commercial C Synthetic C Commeroial D Synthetic D Commercial F Synthetic F
(Cooperators 1 to 6) 2 3 4 5 6 50% ._Solution of Modified Phenolic Resin F+ E E++ E+ E FD CSt 1
.. ‘C
B
T+2B
T+3B D+ C-
.. .C.
u
82
x x+
....
:+
B+iB 60% Solution of Alkyd Resin
C
B/C
Commercial C Synthetic C Commercial D Synthetio D Commercial F Synthetic F 37.5% 0.5-Second Nitrocellulose Solution Thinned 60/40 with Thinners Commercial C Synthetic C Commeroial D Synthetic D Commercial F Synthetic F Aniline Points 40.5 40.6 59.0 59.0 24.6 25.4
39.4 39.6
..
25: 0 25.4
a “F+” indicates a viscosity heavier than tube F. “ F f t B ” , one quarter bubble heavier than F; “ F - + B ” , one quarter lighter than F.
VOL. 11, NO. 5
I n considering the comparative viscosities of resin solutions, the differences in average boiling points shown in Table I11should be noted. The higher molecular weights indicated by the higher boiling ranges of the commercial solvents makes for a higher molal resin concentration in a given resin solution made on a weight basis.
Conclusion The refractive index-sulfuric acid extraction method for determining the aromaticity of commercial high-solvency hydrocarbon thinners, whose evaporation rates are similar to that of toluene and which are substantially olefin-free, provides results which are reasonably accurate, as shown by comparison with synthetic blends, and can be duplicated by several cooperating laboratories with a precision of *0.5 per cent. Although the method, as it stands, does not determine the naphthenic or paraffinic contents with the accuracy or precision which may be desired, the relatively greater importance of aromaticity is demonstrated by a reasonably good concordance in the viscosities of solutions of film-forming materials in the commercial thinners and their synthetic matches. Literature Cited Baldesohwieler,
E. L., Morgan, M. D., and Troeller, W. J., Jr.,
IND.ENG.CHEY.,Anal. Ed., 9, 540 (1937). Baldeschwieler, E. L., Troeller, W. J., Jr., and Morgan, M. D.,
naphtha whose straight aniline point is 60” C., and 10 cc. of anhydrous aniline (4). Each cooperator’s data should be considered per se, since the viscosity of a synthetic resin solution is affected not only by the heat treatment received during solution, but also by the time and method of agitation. Viscosities, expressed in terms of Gardner-Holdt bubble-tube letters, were determined with each cooperator’s own set of standards.
Ibbid., 7, 374 (1935). Kurtz, S. S., and Headington, C. E., Ibid., 9,21 (1937). McArdle, E. H., Chem. & Met. Eng., 44, 598 (1937). McFarlane and Wright, J . Chem. Soc., 1933,114-18. PhiIadelphia P a i n t and Varnish Production Club, “Proximate Analysis of Hydrocarbon Thinners”, Circ. 568, Scientific Section, National Paint, Varnish & Lacquer Association (November, 1938). Thomas, C. L.,Bloch, H. S., and Hoekstra, J., IND. ENQ.C ~ n n i . , Anal. Ed., 10, 153 (1938).
A Modified Beilstein Test for Halogens in Volatile Organic Compounds WM. L. RUIGH,’ Merck & Co., Inc., Rahway, N. J.
D
URING an investigation of the low-boiling fraction obtained in the commercial production of divinyl ether, vinyl chloride was isolated. The need arose for a rapid sensitive test to detect this impurity in the finished product. The well-known Beilstein test (1) for detecting halogens in organic compounds, either with copper oxide in a platinum loop or with plain copper wire, is inapplicable to highly volatile substances and in order to detect vinyl chloride (b. p. -13.9’ C.) in divinyl ether (b. p. 28.3’ C.) the following modification was developed. A piece of clean copper screen 10 cm. square, with about 8 meshes to the inch of fairly heavy wire, is clamped 4 cm. above an ordinary Bunsen burner. The flame is allowed to burn on both sides of the gauze until all trace of green color disappears. The liquid to be tested for halogen is then added drop by drop from ti separatory funnel to a warmed 125-cc. flask through which the gas supply to the burner passes. The presence of halogens is evidenced by the appearance of a green color in the flame. 1 Present address: Department of Physiological Chemistry, University of Pennsylvania, Philadelphia, Penna.
With careful observation in a darkened room the limit of sensitivity was found to be 0.005 per cent of vinyl chloride which corresponds to about 30 parts per million of chlorine. Under the same conditions 0.025 per cent of vinyl chloride gave a strong green flame. Since this paper was submitted, Stenger, Shrader, and Beshgetoor (2) have described a modified Beilstein test which is ideally adapted to the detection of volatile halogen compounds in the air, particularly under the conditions found when leakappear in refrigerator pumping systems. The author’s modification, which was completed in March, 1934, was designed primarily for laboratory use to determine halogens in volatile liquids, but it could also be used to determine halos gens in samples of a gas or air. The sensitivity of both tests is of the same order of magnitude.
Literature Cited (1) Meyer, H., “Analyse und Konatitutionsermittlung organischen Verbindungen”, 6th ed., p. 132,Berlin, Julius Springer, 1931. (2) Stenger, Shrader, and Beshgetoor, IND. ENQ. CFXEM., Anal. Ed., 11, 121 (1939).
