INDUSTRIAL A N D SNGINEERING CHEMISTRY
August, 1923
The differences are larger than the degree of accuracy indicated by Wilson and Barnard. A comparison of the figures for the second group of fuels, studied directly by both methods, shows that direct determination gives dew points in all cases higher than those determined from the equilibrium mixture, although the differences are not quite as consistent as those shown by the first group of fuels. -DEW
Indirect Domestic Aviation.
.........
Cooperative Fuel Research Gasoline A (A-2)
Mixture
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12:l 15:l
;;;; 12:l 15:l 15.4:l 16.4:l
c.
1.0 -4.0 28 24 66 60
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POINT-
Direct
c.
17 11 53.7 51.5
..
Above 75
their vapor pressure determinations too high, might account for the discrepancy. The following features should be observed concerning the method here described: 1-The apparatus can be constructed in the ordinary laboratory and machine shop. 2-With a little practice the dew points may be read with fair accuracy and reproduciblity. 3-It is believed sufficiently direct to be free of large errors. 4-It applies to volatile fuels of any nature.
The method is offered tentatively as suitable for the direct determination of the “effective” volatility of motor fuels, with the idea that it may be useful in studying specifications and blending operations and for the control of distillation tests and other methods of evaluation.
74.5
It may be observed that the range of temperature between the dew points a t 12:l and 15:l varies considerably. ’ The possible errors of the method employed by the author are, as has been mentioned, such as to make the results obtained more probably low than high; some consistent error in the work of Wilson and Barnard, such as errors in the preparation of the equilibrium solution, which would tend to make
799
ACKNOWLEDGMENT The author wishes to express his gratefulness for the helpful suggestions received from W. F. Faragher, Senior Fellow, Petroleum Fellowship, Mellon Institute, and also to S. P. Marley for assistance in the construction of the apparatus used, and to S. P. Marley and R. W. Henry, for assistance in making observations.
Determination of Phenols in Coal-Tar Oils and Crude Carbolic Acid’ By J. Bennett Hill THEBARRETT Co., 40 RECTORST., NEWYORK,N. Y.
of steam distillation of the ROM time to time a The various methods for defermination of phenols or tar acids in original oil, a somewhat great many methods coal-tar oils, such as crude carbolic acid, dip oil, coal-tar flotation elaborate procedure for conhave been advocated oils, etc., have been investigated, special attention being given to centrating the phenols in for determination of actual the contraction method of Weiss, in which the contraction of the the steam distillate into a phenols or tar acids in coaloil on extraction with caustic soda is taken as the per cent phenols. small quantity of benzene, tar oils, such as creosote oil, The claim that this method gives high results has been shown to be and final measurement by dip oil, etc., and in crude without foundation. The liberation methods, in which the tar acids shaking with caustic soda carbolic acid. Where only are extracted from the oil with caustic soda, liberated from the solution and measuring a rough determination has carbolate with acid and measured, give high results when carefully the increase in volume. been required, almost any run. multiplying the result by of these methods is suita factor empirically deterable. A demand for a greater accuracy of determination and closer check between mined, which happens to be the reciprocal of the specific producer, and consumer is, however, frequently made, and gravity of the phenols. Among the liberation methods are included those of it was to meet this demand that this investigation of some Weiss2 (Test H-12), Allen,4 and most of the methods in use by of the existing methods was made. The successful methods for determination of phenols in various industrial laboratories. The methods in general oils and crude acids are all based on their solubility in soda differ only in detail, the liberation method of Weiss differing and their extraction from the oils with a solution of sodium hy- also from the others in that the phenols after liberation are dissolved in refined coal-tar naphtha before measurement. droxide. They may be divided into two main classesIt has been generally believed that the contraction method first, those which use the contraction in the volume of the oil or the increase in the volume of the aqueous soda as the gave results higher than the correct values, and the liberameasure of the phenols; and second, those which liberate the tion methods results lower than the actual but much closer phenols from the carbolate solution obtained and measure the than those obtained by the contraction methods, as is noted volume of liberated acids. The first class may be called the by Weiss in his description of the two methods. The author’s “contraction” methods and the second class the “liberation” experience has failed to bear out this impression, however, methods. Among the detailed methods belonging to the and it was therefore hoped that the present work would throw first class may be mentioned those of Weiss (Test H-11)2 real light on the relative accuracies of the various methods. Since the publication of the contraction and liberation and of C h a ~ i n .Weiss ~ uses a simple repeated extraction of the distilled oil in a specially graduated separatory funnel methods of Weiss, he has found it advisable to make a few and takes the contraction in volume of the oil as the volume changes in the details of their operation, which he has not of phenols contained in it. The method of Chapin consists published. Thus, in the contraction method (H-11) where repeated extraction with 50 cc. of 10 per cent soda is recomReceived March 16, 1923. mended, it has been found simpler and safer to make in every * THISJOURNAL, 10, 913 (1918).
F
8
Bzw. Anzmul I n d u s t r y , Bull, 107.
4
Allen, “Commercial Organic Analysis,” Vol. 111, p . 375 (1909).
INDUSTRIAL A N D EiVGlhTEERIXG CHEMISTRY
800
case three extractions with 100 cc. each of 10 per cent soda. Where the tar-acid content is above 35 per cent it has been found advisable to dilute tNe material with one or three parts of clean, dry kerosene so as to bring it within this limit. The result is of course multiplied by 2 or 4. I n the liberation method (H-12), whereas originally extraction with 50-cc. portions of 10 per cent soda was recommended, it has been found better to make the extraction with 25-cc. portions of 15 to 20 per cent soda, in order to keep down the volume and to wash the carbolate so obtained with benzene before acidifying, thus removing the considerable quantity of oil dissolved by the stronger carbolate. The dissolved benzene is driven off by heat before liberation of the acids. The necessity for making all measurements a t the same temperature has also been shown. It will readily be seen that since the coefficients of expansion of the tar oils are about 0.0007 to 0.0010, a difference of several degrees in temperature between initial and final measurements will make a very considerable error in the results. I n the work described below, in which these methods were applied, the changes noted were used. ANALYSESOF SYNTHETIC MIXTURES The first part of the investigation consisted of the analyses of synthetic mixtures by the various methods. For the preparation of these mixtures a neutral coal-tar oil was used from which the phenols and pyridine bases had been completely removed by extractions with soda and with sulfuric acid. The phenols consisted of a mixture of specially purified, oilfree phenol, o-cresol, and m-p-cresol in proportions to approximate their natural occurrence. Mixtures of the oil and phenols were made up by volume with great care. In order to determine the effect of a less careful purification of the oil used in the mixtures, two mixtures were made from oil in which the pyridine bases were not extracted and the tar acids only roughly extracted. This showed a pyridine-base content of 4.0 per cent and a tar-acid content of 0.3 per cent, the tar acids being determined by a liberation method and being therefore actually isolated and identified as phenols. All these mixtures were analyzed by the modified Weiss contraction method, and some by the modified Weiss liberation method. The results appear in Table I.
Sample 1 2 3 4
5 6
TABLEI-ANALYSES OF SYNTHETIC MIXTURE PHENOLS FOUND Phenols Present VOLUMEP E R CENT Contraction Liberation Volume Method Method REMARKS Per cent .... 3 0 3 0 20 0 20.3 20 0 19 8 20.2 20 2 .... .... 25 0 25 0 .... 25 0 25 2 25.9 25 2 28.0 } Pyridine not extracted 25 2 25 3 .... i 25 5 .... 95.26 I g5 95.6 ...
1 {
1
'
It will be noted from Table I that the results with the contraction method are slightly higher than the theoretical, while the results with the liberation method are still higher. The incomplete extraction of the oil used in the mixtures appears to have very little effect on the contraction method a t least. Duplicate determinations were made by Chapin's method on the 95.26 per cent mixture corresponding to Sample 6. Although the determinations were carried out with the utmost care to avoid loss, check values of 91.0 and 91.0 per cent were obtained. It should be noted that if these results are multiplied by the specific gravity of the mixture a t the temperature of measurement-in this case 1.047-values of 95.3 per cent are obtained, which check well with the theoretical. This would be the logical procedure to obtain volume per cent if Chapin's arbitrary factor were omitted. '
.
1701. 15, Yo. 8
-4NALYSIS O F COMMERCIAL O I L
The fact that the contraction method gives good results on a synthetic mixture of a purified oil and a purified tar-acid mixture, does not necessarily show that it gives equally as good results on a natural coal-tar oil which has not been extracted. Accordingly, determinations were made by both the contraction and liberation methods on two samples of commercial dip oils. The results given in Table I1 show a good check between the two methods. TABLE 11-ANALYSES Sample
7 8.
OF COMMERCIAL OILS --PHENOLS FOUND-VOLUMEP E R CENT-Contraction Method Liberation Method 15.0 15 0 25.6 25.4 25 2
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It was noticed in the course of the work on the liberation method .that in general the lower the volume of carbolate, the higher the final result. This is to be expected from the solubility of the tar acids in the sodium sulfate underlie from the liberation. For example, in the results on Sample 5 in Table I, where results were obtained which are comparatively the highest, the lowest volume of carbolate was obtained. If this method is to be used, the volume and strength of carbolate to be obtained, together with the quantity of sulfuric acid to neutralize, should be standardized. A determination was run on Sample 8 by the liberation method but omitting the dilution of the liberated phenols with the naphtha before reading. A result of 26.5 per cent was obtained as against a mean result of 25.3 per cent obtained with the naphtha. A subsequent dilution of the phenols so obtained with naphtha precipitated out mater to the extent of about 1 cc. corresponding to 1 per cent on the result. Apparently, the omission of the naphtha gives high results due to dissolved water in the phenols. RECOMMENDED I M
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~
The results of this work tend to establish the accuracy of the simple contraction method for determination of tar acids in oils and crude carbolic acid. The method is recommended for general use on coal-tar oils and crude carbolic acids in the following form: APPARATUS-Tar-acid funnel, Type 2,2200-cc. distilling flask; 100-cc. standardized pipet; condenser. REAGENTS-sodium hydroxide, 10 per cent SOlUtiOn. PROCEDURE-A100-cc. sample of the oil a t 25" C. is measured into the distilling flask and distilled to decomposition, the distillate being collected in the tar-acid funnel. The volume of the distillate is carefully read a t 25" C. and, if no solids have separated, is extracted with three successive portions of 100 cc. each of 10 per cent caustic soda solution. I n each case after the soda is added to the oil, the whole is thoroughly shaken and is then allowed to settle completely before drawing off the soda layer. The volume of the residual oil after complete settling is carefully noted a t 25" C. The decrease from the volume of the distilled oil before extraction t o the volume after extraction is the per cent by volume of phenols. In the case of samples containing so much naphthalene as to show separated solids a t 25" C., the temperature of the three measurements may be raised to 40°,or even 60" C., extraction being made also a t the same temperature. If the sample contains over 35 per cent tar acids, the quantity taken for distillation should be cut to 50 cc. or 25 cc. so a s to give not more than 35 cc. of tar acids, Before distillation the material should be made up t o 100 cc. with clean, dry kerosene. The result obtained should be multiplied by 2 or 4 . Where the sample to be tested contains water it should be removed by catching the first few cubic centimeters of distillate in a small separatory funnel containing a little saturated salt solution, separating the water and adding the 011 to the rest of'the distillate in the tar-acid funnel. If no diminution in volume takes place on extraction, a trace of tar acids may be detected by acidifying the soda drawn off and noting the odor.
~
