January, 1928
ISDUSTRIAL A N D ENGINEERING CHE-MISTRY
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of Mexican, Colombian, a n d Venezuelan Crude DESCRIPTION NITROGEN Per cent R. 0. X. 2 Heavy Mexican crude 0.358 Light Mexican crude 0.326 R . 0. X. 3 G . R. X. 10 Mexican heavy crude-mixed type 0.354 R. 0. X. 4 Colombian crude 0.226 G . R. X. 12 Venezuelan crude-mixed type 0.231 R. 0. X. refers to Standard Oil Company of New York, and G . R. X. to Gldf Refining Company of Texas.
Table 111-Analyses SAMPLE No.
that “none of the investigators has accounted for the total nitrogen in various oils by the amount of pyridine bases extracted.” That there is nothing inherent in crude petroleum to interfere with the extraction of bases, were they present, can be demonstrated by the addition of a small amount of an organic base, such as quinoline. Our experiments show that quinoline admixed with petroleum can be regained by dilute In the case of Texas oils attention is directed to the followacid extraction. Of course it is possible that the nitrogen in ing analyses cited by Day:I3 certain types of petroleum is entirely in basic form, but such Jefferson County, Lucas Well-more than 1 per cent nitrogen oils have not come under our observation. [Mabery, Proc. Am. Acad. Arts. Sci., 23, 265 (1901)l. Beaumont Through the cooperation of R. E. Haylett and T. F. Ott, Field-0.92 per cent oxygen and nitrogen [Richardson, J . Franklin of the Union Oil Company of California, there have been Inst., 162, 113 (1906)]. examined in this laboratory nineteen products from the Oleum Our analyses of thirty-four crude oils from the Texas refinery. One of these samples, “asphalt crude;” represents gulf coastal region indicate that no petroleum from this the crude oil from the McKittrick district of California, and section will be found t’orun a3 high as 0.10 per cent nitrogen. from this are produced the various crude distillates, refined Samples investigated in the Texas laboratory from Brazoria, products, and residual asphalt included in the remaining Chambers, Galveston, Harris, and Wharton Counties con- eighteen samples. I n an experiment where equal volumes of form in their nitrogen content to approximately 0.02-0.04 the asphalt crude (containing 0.64 per cent nitrogen) and per cent; whereas specimens from Jefferson, Liberty, and 16 per cent sulfuric acid were employed it was found that Orange Counties were in the main within the limits of 0.055 practically none of the nitrogen was removed from the oil. to 0.075 per cent nitrogen. I n all distillates a part of the nitrogen was in dilute acidsoluble form, but as a rule nitrogen in non-basic form preForm of Nitrogen Compounds Present in Pet:roleum dominated. From these observations the conclusion follows It may not be out of place to note that, contrary to state- that in crude oil the nitrogen compounds are in the main not ments often found in petroleum literature,*J4 we find, a t least basic, but in distillates bases appear along with non-basic as far as California petroleum is concerned, that very little of nitrogen compounds of unknown structure. At this time it the nitrogen can be extracted from crude oil with dilute min- will suffice merely to emphasize the fact that in the case of eral acids. Our observation is in line with Day’s claim15 neither petroleum nor distillates can the nitrogen compounds 1s Handbook of the Petroleum Industry, Vol. I, p. 530 (1922). be quantitatively extracted with dilute mineral acids, and 14 Redwood, “Petroleum and Its Products,” Vol. I , p. 204 (1896); Engler, a method of estimation of nitrogen in these products be deChem.-Zlg., SO, 713 (1906). veloped from this initial procedure. 15 0 0 . cit , p. 529.
Analysis of Mixtures of Similar Organic Compounds‘ F. H. Rhodes, F. T. Gardner, and A. W. Lewis CORNELL UNIVERSITY, ITHACA, N. Y.
NE of the most difficult types of problems in analytical chemistry is the determination of the individual components of a mixture of homologous or isomeric organic compounds. The substances present in such mixtures usually resemble each other so closely that they cannot bt: separated quantitatively by chemical means. Xost of the methods which have been suggested are based upon the relationships which exist between the composition and the physical properties of the mixtures-as, for example, the boiling points, melting points, densities, or refractive indices. Such methods are frequently unsatisfactory and are more or less limited in their application. Frequently the rate of change of physical properties with change in composition is so slight that physical methods of analysis are subject to very considerable error. Furthermore, such methods are applicable only to the analysis of mixtures in which the number of components is small and the identity of each component is known. Method
0
In a great many cases the amount of a particular substance present in a mixture of similar organic compounds can be calculated from the results obtained by determining, by the cryoscopic method, the apparent average molecular weight I
Received June 18, 1927.
of the mixture in two different solvents, one of which is not a component of the mixture while the other is identical with the particular component being determined. When the solvent used in the determination of the average molecular weight is a substance which is not present in the mixture, each component in the mixture dissolves in the solvent and exerts its normal influence in lowering the freezing point, so that the result is the true average molecular weight of the sample. When the solvent used is a substance which is itself a component of the mixture, that amount of that substance which is present in the sample taken for the determination acts simply to increase the amount of the solvent. The other substances dissolve in the solvent and lower its freezing point, the magnitude of the depression of the freezing point depending upon the molal concentration of these other components in the total amount of solvent. From the two sets of results thus obtained the concentration of that particular component in the mixture can be calculated. The equation for calculating the percentage of an individual component from the results of the two determinations of apparent molecular weight may be developed as follows: Let Ma m
= molecular weight of a specific component, A =
average molecular weight of the mixture, as determined by cryoscopic methods using as a solvent
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
86
a substance which is not a component of the mixture w = weight of sample of mixture taken in cryoscopic determination of apparent molecular weight in pure A as solvent N = total number of gram-molecules in w Na = number of gram-molecules of A in N N. = number of gram molecules of substances other than A in N W = weight, in grams, of pure A taken as a solvent in determination of apparent molecular weight Wl = total weight, in grams, of A present in solution of w grams of mixture in W grams of pure A K = freezing-point constant of pure A-i. e., depression of freezing point produ'ced when 1 gram-molecule of solute is dissolved in 1000 grams of A dT = observed depression of freezing point when w grams of mixture are dissolved in W grams of A x = percentage by weight of A in mixture Then N = Na N. Ne = N N, Wi = W A70Ma K A'= dT = l o 3 % K ' ( N N,A = 103 W NaMa lo3 K N - dTW Na = 1O*K M,dT N =W Since n?. .. IOsKw dT W m we have l o 3 K m - M,, mdT Na Ma z = 100 Also W x = - 100 M. 103 K w - dT Wm Therefore w 103 K m M,miT
+ +
-
+
-
+
-
-
.
+
Extent of Application
This method of analysis should be of extensive application, athough not all mixtures of organic compounds can be analyzed in this way. It cannot be used when the substances present are ionized or polymerized, nor is it applicable when chemical compounds are formed between the various components. Furthermore, the method can be applied conveniently only to the determination of substances which have freezing points within the range of temperatures covered by the ordinary Beckman thermometer. It so happens, however, that a great many common organic compounds-as, for example, many of the components of ordinary coal tardo fulfil these requirements. For the analysis of such mixtures this method should prove of considerable value. The method is applicable to the determination of a given component in the presence of any number of other substances, even when the identities of these other substances are not known. Analysis of Mixtures
Vol. 20, No. 1
ficient to depress the melting point of the solvent about 0.6" to 1.2" C. The tube containing the solution was provided with a Beckman thermometer and with a ring stirrer of nichrome wire, and was surrounded by a second tube so as to leave an air jacket approximately 2.5 cm. thick between the sample and the cooling bath. I n order further to minimize supercooling, the bath was maintained 1" C. below the freezing point of the sample. In each case the solution was cooled slowly and with regular stirring until freezing began and the reading on the Beckman thermometer became constant. The solution was then warmed slightly until the crystals disappeared and again cooled and the freezing point again noted. The average of the concordant results of a series of determinations made with the same sample was taken as the true freezing point of the sample. The freezingpoint constants for the solvents used were not taken from the data appearing in the literature, but were determined experimentally with the same lots of material, the same apparatus, and the same procedure that were used in determining the average molecular weights. I n each case the average molecular weight of the mixture was first determined, using as a solvent a substance which was not a component of the mixture. This solvent was usually benzene. but because of the very slight solubility of dinitronaphthalene in benzene, the solvent used for the mixture containing this component was diphenyl. The freezingpoint constants of benzene, diphenyl, and a-nitronaphthalene were determined experimentally, using pure naphthalene as a solute. I n the determination of the freezing-point constant of the naphthalene, diphenyl was taken as the solute. The results are given in Table I. Table I-Freezing-Point
Constants of Components
(Depression produced b y 1 mol solute in 1000 grams solvent)
SOLVENT
O
Table 11-Analysis MIXTURE" h'aphthalene Oil Saphthalene Oil I'-aphthalene Oil
} }
\
of Synthetic Mixtures of Organic Compounds PER CENT m -w LV dT Found Taken 155.9 0.3930 148.2
17 3837
0 962
4.66
4 64
23.25
23 71
0.7162
19.3619
1274
1 4 7 . 2 0.5213
24.0356
0.634 33.45 33.90
]
~ ~ ~ ; ~ ~ ~ & ~ h a1 3l 4 e. 2 n 0.5193 e
~~~~~~~~~~~~~[~~~ }
c.
5.25 7.04 7.71 9.02
Benzene Naphthalene Diphenyl a-Nitronaphthalene
13.3562 2 . 3 8 4 1 0 . 8 8 1 1 . 5 6
1.722 Diphenyl Naphthalene 1 4 0 . 9 0 , 5 6 2 8 27.1955 0 . 6 0 9 Naphthalene Diphenyl 1 5 2 . 4 0.6941 25.0459 0 . 8 2 5 a-Nitronaphthalene Diphenyl 1 6 2 . 4 0.6012 20.4169 0 . 8 8 7 Naphthalene a-Nitronaphthalene I n each mixture t h e component which was determined of which t h e percentage is given is listed first.
}
1 1
217.7
1 , 0 0 4 4 21.4653
8 60
8,78
49.93 49.54 29.45 29.84 40.20
40.65
separately and A number of synthetic mixtures of organic compounds were analyzed by this method. The components of these I n the analysis of a number of synthetic mixtures by the mixtures were naphthalene, diphenyl, a-nitronaphthalene. dinitronaphthalene, and heavy coal-tar oil. The naphthalene, method described above, the results in Table I1 were obtained. diphenyl, and a-nitronaphthalene were purified before use. I n each case the result given is that of a single determination, The dinitronaphthalene was from a purchased supply of although the values taken for the lowering of the freezing supposedly pure material. The heavy coal-tar oil was a point were obtained by averaging a series of concordant naphthalene-free fraction obtained by the careful fractional results obtained with the same solution. The first attempts to analyze mixtures of a-nitronaphthadistillation of creosote oil. It had a specific gravity of 1.030, distilled ct~mpleteiybetween 239' and 303' C., and consisted lene and dinitronaphthalene gave results which indicated a principally of a mi5ture of methylnaphthalenes, diphenyl, much higher content of mononitronaphthalene than was actually taken. Upon examination the dinitronaphthalene, and acenaphthene. I n making the cryoscopic determinations precautions were which was supposed to be pure, was found to contain contaken to secure uniformity of conditions and to minimize siderable amounts of mononitronaphthalene. The dinitro.. supercooling. A fairly large quantity (13 to 27 grams) of naphthalene was then purified by repeated extraction with the solvent was weighed into a large test tube (2.5 cm. benzene. The analysis of mixtures of the purified material diameter) and a weighed quantity of the sample to be analyzed with known amounts of mononitronaphthalene gave satiswas added. The amount of sample added was usually suf- factory results.
