V O L U M E 2 6 , NO. 2, F E B R U A R Y 1 9 5 4 ACKNOWLEDGMENT
The authors appreciate the assistance of Mary-Anne Morris in obtaining the complete spectral curves of the sulfuric acid chromogens. LITERATURE CITED
(1) Diaz, G., Zaffaroni, A., Rosenkranz, G., and Djerassi, C., J .
Org. Chem., 17, 747 (1952).
329 (2) Wall, M. E., Krider, 11. AI., Rothman, E. S Iand Eddy, C. R., J . Biol. Chem., 198, 533 (1952). RECEIVED for review August 20, 1953. Accepted October 19, 1953. S i n t h in a series on steroidal sapogenins. Work done a s part of a cooperative arrangement between the Bureau of Plant Industry, Soils, and .%vicultural Engineering and Bureau of hgricultural and Induatrial Chemistry, U. S. Department of Agriculture and the National Institutes of Health, Department of Health, Education, and Welfare.
Rapid Determination of Aromatics in Petroleum Absorption with Picric Acid-Nitrobenzene EDUARDO A. PASQUlNELLl Destileria de Yacimientos fetroliferos Fiscales, f u e r t o Eva feron, Argentina
A rapid and simple method has been developed for determining the aromatics in a wide variety of petroleum fractions boiling below 600" F. With this method a pair of determinations can be performed in only 20 minutes, using not more than 10 ml. of sample and a minimum of equipment. Its precision is io.;% and its accuracy is of the order of =kl?6. The method is specific for aromatic hydrocarbons. Olefins do not interfere, and thus i t can be applied directly to cracking products without an additional determination, such as bromine number, which is often necessary in many of the existing methods. Furthermore, the test furnishes qualitative information.
M
ANY different methods have been reported for the quanti-
tative determination of aromatics in petroleum fractions. They are most varied and include such techniques as sulfonation (18), nitration (IO), hydrogenation (IQ), oxidation (Q),solubility (II), absorption (6), aniline points ( 9 ) , silica gel adsorption ( 1 7 ) , chromatography ( 7 ) , refractive index and specific dispersion (21), ultraviolet spectrometry ( d ) , and Raman spectrometry (IS). Several of these methods involve the use of more than one technique. Although many of these methods have good features and represent great progress in hydrocarbon analysis, none of these possesses all the advantages that one would wish to see in a single analytical method. Some of the methods need very expensive instruments, and most of them are not specific for aromatic hydrocarbons and need complementary determinations such as bromine number, to correct for olefins. Sone of them is general, they cannot be applied indiscriminately to any petroleum fraction, and sometimes they are complex, laborious, and timeconsuming. Furthermore the petroleum industry lacks an easy test to disclose the presence of aromatics. Many of these methods are useful in industry, and some have become standard procedures, but the ideal of accuracy, precision, rapidity, simplicity, specificity, generalness, and economy has not yet been attained in this field. It was decided to investigate the possibility of developing easier and simpler qualitative and quantitative analytical methods for determining petroleum aromatics. The action of picric acid upon petroleum distillates was tested, taking advantage of its ability t o form molecular combinations with aromatic hydrocarbons. These addition complexes are colored and crystallizable, with characteristic melting points that can be used to identify the respective aromatics. Huntress and Mulliken (14) cite many examples of these complexes. The predominating colors are yellow, orange, and red, and in general the picrates are molecular combinations of 1 mole of picric acid for each mole of hydrocarbon. A4nexception is anthracene which, apart from its normal combination, forms another complex of 2 moles of picric acid for each mole of hydrocarbon. Certain aromatic
hydrocarbons such as diphenyl and diphenylmethane forni no true picrates. A survey of the literature revealed that picric acid has seldom been used in the petroleum industry for analytical purposes. Few investigations of picric acid aa an analytical reagent for hydrocarbons have been undertaken. Jones and Wootton ( 16 ) in 1907 identified 1- and 2-methylnaphthalene in a 180' to 210' C. fraction of a Borneo crude through its picrates. Cosciug (8) in 1935 separated picrates of both methylnaphthalenes from a 30"
5w 10 I
1 P 3 4 5
I
10
I 15
REAGENT ADDED, VOL. %
Figure 1.
Influence of Reagent Concentration on Color of Challaco Kerosine6 1. 10% picria acid in nitrobenzene 2. 3. 4.
15% picric acid in nitrobenzene 20 % picric acid in nitrobenzene 55% picrio acid in nitrobenzene
to 200' C. fraction of a Romania crude. I n 1946, Gambrill and Martin ( 1 1 ) developed a method for' the determination of aromatics in gasoline based on the variation in the solubility of picric acid with the change of aromatic content. Sachanen (80) mentions the use of picric acid in separating
ANALYTICAL CHEMISTRY
330 Table I. Test of the Reagent on Different Petroleum Samples and on Some Pure Hydrocarbons
Product Naphtha, straight run
Caleta OliJia Barrancas Manantial Behr Venezuela San Lorenzo Lujan de Cuyo Chachapoyas Caliadon Perdido Comodoro Rivadavia Iran Challaco Ecuador Comodoro Rivadavia Cafiadon Perdido Cafiadon Perdido
EleotroColor Obtained photometric by Adding 5% Color (Green Reagent Light, Microcell) ... Colorless Colorless Colorless .. .. .. Pale yellow ... Pale yellow ... Orange ... Intense red .. .. .. Orange Yellow 20.0 Pale yellow 14.0 Orange 38.0 Yellow 21.0 Orange red 72.0 Orange 30.0 Pale yellow 13.0 Pale yellow 12.5 Pale yellow 16.0 Orange 30.0 Pale orange 26.0 Orange 31.0 Orange 39.0 Yellow 23.0 Ruby red ... Ruby red ... Red ... Orange red ... Orange .. . .. Red Reddish orange ...
Caiiadon Perdido Cafiadon Perdido Cafiadon Perdido
Ruby red Ruby red Intense red
...
Cafiadon Perdido Cafiadon Perdido Tupungato Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Cafiadon Perdido Caleta Cordoba C hallac o Challaco Peru Peru Peru Peru Iran Iran Iran Iran Challaco
Dark red Very dark red Colorless Yellow Yellow Pale yellow Yellow Yellow Yellow Orange Orange Yellow Pale yellow Yellow Yellow Red Red Orange red Orange red Orange
... ... ...
Comodoro Rivadavia
Colorless
Comodoro Rivadavia
Colorless
Comodoro Comodoro Comodoro Elaborated
Colorless Intense red Red Colorless
Origin of Crude Comodoro Rivadavia Challaco Iran Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Comodoro Rivadavia Challaco Peru (HCT) Iran
Naphtha, cracking Solvent Agricol Kerosine
Kerosine mixture Kerosine
Kerosine mixture
Gas oil
Cut (215°-3000C.) Light oil (contacted) Light oil (Edeleanu contacted) Li h t oil (Edeleanu, contacted, iewaxed) Medium oil (Edeleanu, contacted, dewaxed) Medium oil (contacted) Heavy oil (Edeleanu, contacted, dewaxed) Edeleanu extract of medium oil Paraffin Kerosine
Kerosine (extracted: 3% aromatics) Cut (207°-2580 C.; extracted; 2.5% aromatics) Light oil (extracted: 1% sulfonatables) Light oil (21% sulfonatables) Medium oil (11% sulfonatables) n-Heptane Iso-octane (2,2,4-trimethylpentane) Cyclohexane Benzene Xylene Xylene plus 1 % naphthalene Xylene plus 1 % fluorene Xylene plus 1 % phenanthrene Xylene plus 0.5% anthracene
Rivadavia Rivadavia Rivadavia cut
Elaborated cut Pure cut Pure cut Commercial
... ... ...
...
Colorless Colorless Colorless Pale yellow Yellow Yellow Yellow Orange
aromatic hydrocarbons in a petroleum fraction and says that it is surprising that such a method has not been used more widely. However, in his method five or ten consecutive treatments are needed to attain a total separation of the aromatics. Apart from being tedious, this would make quantitative determinations a problem because of excessive handling. More recently, Godlewicz (1%) developed a ChromatWraPhic method based on the adsorption by silica gel of the aromatics of a lubricating oil, using trinitrobenzene as indicator in the chromatographic column. Characteristic CO~ors appeared in the zone in which the aromatics were adsorbed. Godlewicz also tried other aromatic polpitro compounds as chromatographic indicators, picric acid among them. QUALITATIVE T E S T S
Picric acid dissolved in nitrobenzene was used in the qualitative tests conducted in this laboratory. Xitrobenzene was chosen
...
...
18.5 17.0 14.0 22.0 23.0
19.0 45.0 41.0 21.0 10.5 25.0 15.0
NP-4 Color 1 11 1-1.5 1-1.5 4 Above 8 4 2.5 2-2.5 3.5 2.5 4.5 3 2-2.5 2-2.5 2-2.5 3 Below 3 3 3.5 2.5-3 5-6 6 6-7
5 4 6-7 4.5-5 5-6 6 7-8 8 High above 8 1
2.5 2.5
2-2,5
2.5 2.5 2.5 3,5-4 3.5 2.5 2 2.5-3 2-2.5 4.5-5 4.5-5 4 4-4,5 3
because in addition to being an excellent solvent for picric acid, the solution of picric acid in nitrobenzene has stable chemical and physical properties. This was the first reagent found to give qualitative results. A concentration of 20 grams of picric aci.1 in 100 ml. of nitrobenzene was used because it gives the highest intensity and characteristic colors (plateau colors). Choice of this concentration was based on Figures 1 and 2. The reagent proportion chosen was 5% of sample volume. Figures 3 and 4 show that this proportion is the most convenient to render characteristic plateau colors independent of molecular weight, refinement step, and aromatic content of the sample.
Procedure. Twenty milliliters of petroleum fraction (naphtha, kerosine, gas oil, or lubricating oil) was shaken in a test tube with the reagent for 10 seconds. After 10 minutes, the color was observed and measured. The results are shown in Table I. The colors were measured with a Fisher electrophotometer and also with a Union colorimeter (3). The correlation between bothkindsof color measurements can be seen in Figure 5 .
The observed colorswerestable, as shown in Table 11. They were also free from any inter58.0 31.0 ference, as shown in Table I11 and Figure 6. Concentration of 6.5 1 1 the aromatic fraction could be ... computed from the measurement 1 ... of the color intensity because ... 7-8 .6.0 .. 6-7 Beer's law was valid (Figure 7 ) . 1 Because of its color reactions, ... 1 the reagent discloses the presence ... 1 .. .. .. 1.5 of aromatics in apetroleumdistil1.5 ... 1.5-2 late and makes possible an esti1.5-2 ... mate of the amount of aro... Below 2 ... 3.5 matics present. It also gives information on the refinement step, sometimes indicates the origin of the crude, and permits quantitative calculations in the particular case of a fraction in different extraction grades. 88.0
85.0 53.0
QUANTITATIVE T E S T S
It was evident that measurement of the color reactions would not yield further information because they depend not only on the amount of aromatics but also on their molecular weight and their structure; simple isomeric differences different color reactions, as can be seen from a comparison of anthracene and phenanthrene in Table I. Therefore, it was not possible to base upon the colors of the picrates. general quantitative To overcome this obstacle, another property observed in handling picric acid-nitrobenzene reagents was investigated. It can be seen in Figures 1, 3, and 4 that a quick rise of color takes place; afterward around 5 % there is a region of constant color (plateau color) followed by a slow rise. In the tests t'hey represent, if reagent was continually added, a separation of the liquid
V O L U M E 26, NO. 2, F E B R U A R Y 1 9 5 4 A0
33 1
!-
10 15 PO 30 40 50 60 CONCENTRATION OF REAGENT, GRAMS IN 100 ML. OF SOLVENT
Figure 2. Plateau Colors of Challaco Kerosine Treated with Reagents of Varying Concentration
Table 11. Effect of Time on Stability of Color Resulting from Test of Aromatics
This expression is termed the F function. The function is valid with a probable error of &0.7% when working a t 20" 0.5" C. with reagent of 21.75% on samples of molecular weight between 100 and 400 and aromatic content up to 25%. For molecular weights under 100, the straight line becomes curved toward the abscissa. For molecular weights over 400 the straight line becomes curved toward the ordinate. These molecular weight limits cover the wide range between naphthas and medium lubricating oils including kerosines, gas oils, and light oils. Even samples beyond the molecular weight limits can be resolved by means of adequate dilutions. The proposed method deals only with petroleum fractions that boil below 600' F. The heavier cuts such as gas oils and lubricating oils give values practically in agreement with the percentage sulfonatable ( I ) which is undoubtedly related to the aromatic content. A future publication will discuss the application of this method to heavy distillates.
Electrophotometric Color Comodoro Rivadavia keroyine Challaco kerosinr 14.0 34.0 13.5 34.0 12.0 33.0 11.0 33.0 11.5 32.5 12.0 31,s 13.5 34.0 14.0 35.0 13.5 34.5 13.5 35.0 ~~
Interval between Test and Color RIeasurement 10 minutes 30 minutes 60 minutes 2 hours 3 hours 24 hours 3 days 7 days 17 days 35 days
in two layers sharply defined by a meniscus could be observed in the region of 15 to 20%. The lower layer, strongly colored yellow, orange, or red, was composed mainly of nitrobenzene and picrates of aromatic hydrocarbons. The upper layer, weakly colored in the same hues, was composed mainly of nonaromatic hydrocarbons. On this experimental basis it was possible to develop an absorption method by controlling the concentration and volumetric proportion of reagent with respect to the sample. Starting from a given volume of sample and extracting with a certain volume of reagent of certain concentration, the volume diminution of the hydrocarbon (upper) layer was a measure of the aromatic percentage initially present in the sample. A quantitative method was thus established for the rapid determination of aromatics in kerosine using a 30% reagent (grams per nil. of solvent) added in a volumetric proportion of 8 to 7 with respect to the sample. Comparison of this procedure with the Institute of Petroleum ( I P ) method (15) showed differences of only *1%; the procedure could be performed in only 15 minutes. mith slight variations it was possible to generalize the method for other petroleum distillates. Previous tests had shown that lubricating oils needed more reagent than kerosines and these more than naphthas. The amount of reagent needed to produce absorptions representative of the aromatic content of the sample depended in some way on the molecular weight or some variable related to it, such as density, distillation curve, or viscosity. Density proved to be of no use, because it did not lead to simple functions. The distillation curve was not easy to apply in lubricating oils, and viscosity could not be used for light distillates such as naphthas and kerosines. Finally it was established that molecular weight was the factor providing the key to the problem The amount of reagent is a simple function of the molecular weight. Although such functions give increasing curves with molecular weight and also depend upon the reagent concentration, a 21.75% reagent (grams per 100 ml. of solution) has a linear variation (Figure 8) whose analytical expression is
R/H
= 0.004 A !
lot 1
Figure 3. 1. 2. 3. 4.
1
1
1
1
P
3
1
I
I
15
Independence of Reagent Proportions from Aromatic Contents Comodoro Rivadnvia kerosine. 9.7% a r o m a t i c s Peru kerosine, 11.770 aromatics Challaco kerosine, 23.0Cj'caromatics Iran kerosine, 17.7% aromatics
Table 111. Effect of Prior Treatment of Kerosine on Resulting Color Origin of Crude Iran
Challaco Comodoro Rivadavia
Peru Iran
Laboratory Treatment Untreated 570 soda, s a t p r wmh Contacted at 150' C. Untreated 3 % sulfuric acid (98%), three stages Entreated Contacted a t 160° C. Furfural extraction Untreated Contacted a t 150° C. Untreated Distillation with 99% yield Untreated Distillation with 98% yield Untreated (sodiim plumbite test negative: doctor test positive) 3 % hypochiorite until doctor was negati vc
+ 0.4
where R is the reagent volume in milliliters, H is the sample volume in milliliters, and M is the molecular weight of the sample.
1
4 5 10 REAGENT ADDED, VOL. %
Coniodoro Riradavia
Doctor treatment, filtration, water ' wash Addition of 1% 0 . 1 N soda solution Addition of 1 % 0.1N hyd,rochloric acid Addition of 1% pure acetic acid Furfural extraction Untreated Furfural extraction
Electrophotometric Color 85 85 85 58 50
38.0 36.5 6.5 18.5 17.5 15.0 13.5 21 0 21.0 80 an ""
80 77 75 77 6.0 13.5 6.5
ANALYTICAL CHEMISTRY
332 For aromatic contents above 25%, use of the F function may give values with large errors; but the 0 to 25% zone is broad enough to permit the resolution of the great majority of cases. Samples out of this limit can be resolved by diluting with a fraction of similar molecular weight and low aromatic content. The F line is also affected by temperature since absorption increases with temperature. The chosen temperature of 20" + 0.5' C. causes errors only of the order of &0.2% in aromatic content.
It I
I
I
I
I
I
I
1
1
10 PO 30 40 50 60 70 80 90 MEASURE OF C O L O R IN FISHER ELECTROPHOTOMETER (Green Light, Microcell, Conventional Zero)
100
Figure 5 . Relation between NPA and Electrophotometric Colors 9 1 -
I
I
I
I
t
I
1. Iran gas oil 2. Comodoro Rivadavia contacted light oil 3. 4.
Furthermore, nitrobenzene vapors are toxic and must be handled in a well-ventilated room or better under a hood. Care must also be taken against the action of the reagent upon the skin and clothing. The reagent must be tested with pure hydrocarbon mixtures, following the procedure. The amount of reagent to add will result from the molecular weight calculated for each mixture. A 10% mixture of toluene in n-heptane can be used, the resulting aromatic content of which must be 10.0 f 0.5%. Similarly with :t 10% mixture of 1-methylnaphthalene in n-hexadecane a content of 10.0 & 0.5% must be present.
Comodoro Edeleanu contacted dewaxed light oil Comodoro Rivadavia contacted viscous oil
. 0:
The reagent concentration (21.75% grams per 100 ml.) that satisfies the F function happens to be 1 mole of picric acid for every 10 moles of reagent (picric acid plus nitrobenzene) or a 10% molar concentration of reagent with respect to picric acid. This 10% molar reagent is the one which provides the most satisfactory practical results compared with all the other proportions. For higher concentration reagents the F linear function becomes increasingly curved toward the ordinate. This effect is stronger in more concentrated reagents. For more dilute reagents the F function becomes random, since absorptions are no longer a direct expression of the aromatic content. The constants of the F function have a very simple relation to each other. Ordinate intercept value (f)/slope ( K ) = 0.4/0.004
=
100
In short, the F function or its graph permi.ts the easy and simple determination of the aromatic contents of petroleum fractions. All that is necessary in practice is to add the amount of reagent indicated by F and, after the recommended experimental procedure, to read the absorption of the sample in the reagent. This gives the aromatic content. METHOD
Materials. Picric acid, preferably c.P., although technical grade will do. Iiitrobenzene, preferably c.P., although technical grade will do. Test tubes of 30-ml. capacity graduated in 0.1 or 0.2 ml. Suggested dimensions are 25 cm. in length and 14 mm. in internal diameter. Thermostated bath a t 20" rt 0.5" C. Lacking something better, a simple container of about 2 liters filled with water will do. The temperature can be kept constant by adding small amounts of hot or cold water. Pipets, thermometers, and other laboratory apparatus. Reagent. V'eigh 217.5 i 0.1 grams of anhydrous picric acid previously dried in an oven for 24 hours a t 115' C. and allowed to cool to 20" C. Transfer to a calibrated 1-liter flask and add nitrobenzene, stirring a t room temperature until totally dissolved. Dilute exactly to the 1-liter division, a t 20 f 0.2' Filter under vacuum to eliminate any residue and keep the finished reagent in a dark bottle with ground-glass stopper. When preparing the reagent it must be remembered that picric acid may explode from violent shocks, especially when hot.
c.
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30 40 50 OF DISTILLATE
l
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60
70
I
80
~
90
Figure 6. Color Distribution in Kerosine Fractions Tested with -4ro1naticReagent 1. 2. 3.
4.
Comodoro Rivadavis Peru Challaco Iran
Finding Mean Molecular Weight of the S-ple. If the sample is a light distillate such as naphtha, kerosme, or 'et fuel for which the American Society for Testing Materials (ASTM) distillation curve (10% to 90%) is avai2ab!e as.well as its density at 15" C. (60" F.), its mean molecular weight is found through the methodof Watsonand Iielson ( 2 2 ) . Thi!methodrequiresprevious knowledge of the molecular average boiling temperature from the volumetric average boiling temperature and a correction term from the slope of the ASTM distillation curve between 10 and 90% of distillate. These are found by means of an adequate graph of the above procedure as explained in the literature (6,%%). Determination of Aromatics. If the molecular weight established according to the above procedure ie above 100, the sample can be analyzed a8 is. If the calculated molecular weight is less than 100, dilute the sample with a heavier fraction of known aromatic content in order to obtain a mixture above this limit. The molecular weight of the mixture can be computed additively from the molecular weight of its components. In a 30-ml. test tube with 0.1- or 0.2-ml. graduations, place approximately 10 ml. of sample previously dried with calcium chloride or filtered through cotton. Close the tube with a rubber stopper and place in the thermostated bath a t 20" =I=0.5" C. for 5
gen compounds) separate completely in less than 10 minutes.
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~
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~
l
l
300
l
~
~
l
350
/
l
,
koo
Figure 8. Variation of Molecular Weight of Sample with Reagent Volume Added to Sample to Obtain Absorption Numerically Equal to qromatic Hydrocarbon Percentage S . Absorption A . Aromatics R . Reagent H . Sample M. Molecular weight of sample T. Temperature k. Constant AR S = k - (for wnstant T) MH AF tg a = = 0.004
rw
This expression (incomplete in constants) shows that for S = .4 (absorption numerically kR R 1 R
equal to aromatic content) - = 1 and E = M so that - = is the linear function of molecuMH H lar weight
CASES NEEDING PREVIOUS DILUTIONS
,
The procedure described above gives directly in many cases the percentage of aromatics. Kevertheless, the results may be / , l , . , abnormal or there may be interference in the case of certain samples. Because of this these samples must be suitably diluted prior to the test' If after the regular procedure is completed the results are above 25%, they may be in error. I t has been found that above 25% the absorptions may be higher than the actual aromatic content. In these cases the sample must be diluted with a fraction of similar molecular weight and low aromatic content or, better, with a pure paraffinic hydrocarbon or a mixture thereof having a molecular weight similar to that of the sample. This is done in such a way as to obtain an aromatic content below 25% in
ANALYTICAL CHEMISTRY
334 Table IV.
Limits of Error, % +0.5-0.5 +0.5$1.0
-0.5-1.0 + l . G +1.5 -1.-1.5 +1.5+2.0 -1,5-2.0 1 2 . G zt3.0 @ .3 * A5.0 * 5 . G 3Z7.0 zt7.G-110.0 3=10.&3Z15.0
Comparison with IP Method Straightrun and Kerosines cracking and Jet naphthas jet fuels fuels 12 10 3 5 1 3
0
of comparisons 22 25 4 Results from Table V. b Results from Table VI. Results from Tables VI1 and V I I I .
Statistical Distribution of Errors between Methods Number of Samples in Each Error Zone Straight-Run and Kerosines, Jet Fuels, and Cracking Naphthas5 Hydroforming Productsb CopCqmparison cqm- cOm- parison of ~p CqmConiof I P parison parison method parison parison method with with with with with with IP ASTM ASTM IP ASTM AST.M method method method method method method 2 0 1 1
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the mixture. The aromatic content of the sample is obtained by simple arithmetic. The use of pure paraffinic hydrocarbons as diluents instead of petroleum fractions poor in aromatics has the advantage of introducing fewer errors in the computations. The data concerning their molecular weight and aromatic content (0%) are theoretical and therefore without error. At the same time, since the aromatic content of the diluent is O%, smaller amounts of it are needed for dilution; this also means fewer errors in the calculations. However, the dilution with pure paraffinic hydrocarbons must be performed with special care regarding the selection of molecular weight. Even in the zone between 0 and 25% aromatic content it may be necessary to dilute because of the possibility that the experimental results obtained in the direct determination were affected by some error. This may be due to the abnormal absorption of some hydrocarbons (usually the light ones belonging to the range of naphthas) or to the presence of high amounts of olefinic, naphthenic, or isoparaffinic hydrocarbons, the interfering capacity of which has been proved experimentally. It has also been proved experimentally that the interference effect of those hydrocarbons disappears through dilution. Therefore, in practice, it is sufficient to dilute with a normal paraffinic hydrocarbon to eliminate the interference. In general, for any of these three families of hydrocarbons, the interference effect disappears when they are in concentrations under the order of 20 to 30%. In any sample, there is always an uncertainty as to whether the content of interfering materials is below its critical concentration or not. It is therefore suggested that after the direct determination all the samples be diluted, including those showing aromatic content less than 25%. The most satisfactory procedure in every case is to perform stepwise dilutions until two of them give a constant value in the percentage of aromatics; these constant values must be within the order of precision of the method. The convenient proportion of diluent may be successively 20, 40, and 60%. When dealing with natural samples such as petroleum distillates that generally are balanced mixtures of different components, the interference cases are infrequent; in most cases such samples can be resolved directly without previous dilution. This is particularly true for straight-run or topping distillates, especially kerosine or similar cuts, but naphthas may introdure problems of abnormal absorption because of their low molecular weight (100 to 120) which is near the applicability limit of the method (molecular weight of 100). This situation does not arise with cracking fractions (olefins), laboratory samples, or samples
Pure hydrocarbon mixtures< 42 3
Total Number of % Samples Samples in Each in Each Zone Zone 47.2 24.4
0 0 0
85 22 22 15 5 13 3 7 4 1 2 1
65
180
99.8
7
4
0 6
0 3 0
11.1 8.9 3.9 2.2 0.5 1.1 0.5
coming from other processes in which a family of hydrocarbons or even only one of them may prevail thus interfering and making unavoidable a dilution with normal paraffins in each case. hfixtures very rich in normal paraffinic hydrocarbons may give some error because of the slight absorption, of the order of 1to 2%, that they show ip the presence of the reagent. It is then advisable to dilute these samples having less than 5% aromatic content. Furthermore, when dealing with light distillates (naphtha range) the safety limit can be carried to 10%. In these cases the diluent must be a mixture of pure hydrocarbons rich in aromatics, such as 80% of a normal paraffin with 20% of pure aromatic. Petroleum fractions seldom have less than 5% of aromatics and the above mentioned case is infrequent in practice, but when working with artificial samples or light distillates of the naphtha range, the above mentioned precautions must be taken. The expression similar molecular weight used in describing the procedure must be understood to mean a molecular weight
Figure 9.
Flask to Drain Thermostated Reagent
S. Siphon, capillary 3-mm. internal diameter T. Tube L. Stopcock R . Picric acid-nitrobenzene reagent
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not differing by more than 40 or 50 below or above the molecular weight of the sample when diluting with petroleum fractions. When diluting with pure paraffinic hydrocarbons it is always necessarv to attain mixtures whose aromatics have molecular weights lower than the nonaromatics because this is typical of petroleum fractions for which the method has been devised. The molecdar weight of the paraffinic diluent must generally be selected around 20 to 80 units higher than the molecular weight of the sample. If different aromatic percentages result from two stepped dilutions with diluents of different molecular weights (indicating a relationship between aromatic perrentage and molecular weight of the diluent), a third and even fourth dilution must be performed with diluentsr having other molecular weights. The acceptable result will be that having constant values of aromatic content for two stepped dilutions, since the aromatic percentage obtained must be independent of the molecular weight effect of the diluent. Ai practical rule is to obtain consistent results with diluents of higher molecular weights than that of the sample. In all those cases in which a dilution is necessary it must never be excessive because the mere computation of the dilution can cause an increase in experimental error. Thus, when an uiikrioan sample is diluted with 50% of a fraction whose aromatic percentage is known within certain limits of error and after the aromatic content of th,e mixture has been determined experimentally (which will be affected by another error), the computations will triple the initial error. This effect increases with higher dilutions, and it is necessary to take extreme care with the factors that alter precision and always take the mean of several determinations. A b a general rule, the sample for test must be diluted as little w possible. The increase of error originates through working with approximate data in computations of the following kind. C(A ie) ( 1 - C) X ( B i e ) = .W i e where C is conrentration, e is error, and .4,B, and ;lL are aromatic percentages.
+
CALCULATION OF WEIGHT PERCENTAGE OF AROMATICS
When the volume percentage of aromatics is to be converted to weight percentage the following equation is used. Weight percentage aromatics = volume percentage aromatics X density of aromatics density of sample
338
ANALYTICAL CHEMISTRY
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The quotient density of aromatics/ density of sample has the following average values, Naphthas, 1.100 (takisg 0.745 as the mean density and 0.820 as that of the a r o m a t i c s ) . Kerosines, 1.150 (taking 0.800 as the mean density and 0.920 as that of the aromatics). The use of these average values introduces errors not above ~ k 0 . 5 7 ~ which can be somewhat lowered by using in each case t h e e x p e r i m e n t a l value of the sample density. QUALITATIVE OBSERVATIONS
r g
0
-o o -q u
u
10
- M
yy q j mo
010
m N
m W
During the quantitative test both liquid phases change their color, and the observation of these changes in the lower as well as in the upper layer may give information of a qualitative nature, since the colors are due to the picrates of the a r o m a t i c hydrocarbons and depend, apart from their c o n c e n t r a t i o n , on their structures and molecular weights. Generally yellow, orange, and red colors appear with all their interm e d i a t e hues. Sometimes greenish or brownish tones appear. They may be s t a b l e o r u n s t a b l e colors, a n d t h e lower layer is always more intensely colored than t h e upper one. These colors can be readily observed or they can be measured with a colorimeter or electrophotometer. Pure, clear colors of yellow, orange, and red shades indicate samples of primary distillation or straight run. These colors are always perfectly s t a b l e , r e m a i n i n g constant for months. They are comparable with an N P A scale, a n d t h e r e fore can be measured with a Union colorimeter according to the ASTM method (3). D i r t y colors with greenish or brown hues
ANALYTICAL CHEMISTRY
340
Table VIII. Behavior of Reagent w i t h Different Aromatic Concentrations, a n d When Their Molecular Weight Varies w i t h Respect to That of Nonaromatic5 Sample 1 2 3 4
5 6
7 8 9 10 11
1”
Calcd. Afomatic Content, Volume SI
Composition of Sample, M I . Benzene 0.2
n-Heptane 9 8
0.5 1.0 1.5 2.0 2.5
9.5 9.0 8.5 8.0 7.5
Toluene
n-Heptane
0.2 0.5 1.0 1.5 2.0 2.5
9.8 9.5 9.0 8.5 8.0 7.5
2.0 5.0 10.0 15.0 20.0 25.0
9.8 9.5 9.0 8.5 8.0 7.5
2.0 5.0 10.0 15.0 20.0 25.0
*
2.0 5.0 10.0 15.0 20.0 25.0
M,ol.
Reageni VOl. Added,
Absorbed Vol
Aromatic Content, Vol. %
Error,
99.5
8.0
0.25-0.3
2.5-3.0
+0.5
98.9 97.8 96.7 95.6 94.5
8.0 7.9 7.9 7.8 7.8
0.55 1.0-1.0 1.5 2.0 3.3
5.5 10.0-10.0 15.0 20.0 33.0
f0.5 0.0 0.0 0.0 +8.0
99.8 99.6 99.2 98.8 98.4 98.0
8.0
0.35 0.55 1.0 1.5 2.0 2.7
3.5 5.5 10.0 15.0 20.0 27.0
+l.5 +o 5 0.0
0.4
4.0 7.5 10.0 15.5 23.0
+2.0 +2.5 0.0 f0.5
42.0
Mean Cornposition and Interferences
Weight
I
Verylight samples; belowmol. wt. = 100 limit In the limit of 25yo aromatics
Little effect of bad mol. wt. relation
‘In the limit of 25% aromatics
MI,
M1.”
%
+1.0
8.0 8.0 8.0 7.9 7.9
0.0 0.0 +2.0
o-Xylene 13 14 15 16
17 18 19
0.2 0.5 1.0 1.5 2.0 2.5 3.0
7 0 Hexadecane
20 21 22 23 24 2.5 26
0 2 0 5
1 0
1.5 2 0 2 5 8 0
3 0 3 0 3 0
8.0 3 0 3 0 a 0
31 32 33 34 35
a f;
87
Strong effect of bad mol. wt. relation Strong effect of bad mol. wt. relation: and also in aromatic limit Strong effect of bad mol. wt. relation and beyond aromatic limit
30.0
6 H 0 R
8 3 0
I,
0
4
.i
.>
-10
2 0 5.0 10.0 15.0 20.0 25.0 30.0
i Good iiiol. wt. relation
{
I
1 Good
0.2
0.5
1.0 1.5 2.0 2.5 3.0
4 0
9.8 9.5 9.0 8.5 8.0 7.5 7.0
2 0
Good mol. wt. relation Good mol. wt. relation Good mol. wt. relation, b u t beyond aroinatic limit Good iiiol. wt. rrlation, b u t tieyond arorriatic lirnit
40.0 2.0 5.0 10.0 15.0 20.0 25.0 30.0
mol. wt. relation, but beyond aro-
matic limit
10.0 20.0 30.0
4.0
8.0
8.0
ig;:; 100.9
8.0 8.0 8.0
0.75 1.0 1.55 2.3
101 5
8 1
4 2
101.2
f3.0
+17.0
Total solubility
101 8
8 1
137.9 138.1 138.4 139 138.7 139.3
9.5 9.5 9.5 9.6 9.5 9.6
0.3 0.6 1.0 2.0 1.55 2.5
3.0 6.0 10.0 20.0 15.5 25.0
+I
134.6
9.6
H 0
36.0
+G
10.0 19.5
n-Heptane
27 28 29 30
100 1
Strong effect of bad mol. wt. relation
I
/High luol. wt. of nonaromatic fraction willpared to aromatic fraction I
(Strong rffect of bad mol. wt. relation
I
1,;1 1.52
10.0
10.1
1 0 1 95
132 :4
10.1
:1.03
163
IO. 1
,> 0
223.6 220 214 208 202 196 190
12 !I 12.8
0.25 0 4.5
12.6 I2 3 12.1 11.8 11.6
_ _
0.9:,
1 4 1.65 2.1
2 55
+0.5
0 0
Procedure for Qualitative Test. Shake 20 ml. of sample Rith 1.0 ml. of reagent vigorously in a test tube for 10 seconds. In this case a single colored phase is obtained. After 10 iniiiutes’ settling, following previous filtration if there are crjstals or turbidity, the color of the clear liquid can be observed or measured. In the prescribed working conditions, the color obtained is rharacteristic in tone and intensity of the cut or sample tested and depends only on the amount, molecular weight, and strurture of the aromatics present. These colors, apart from being free of interferences, make ~ O E sible the calculation of concentrations because they satisfy Beer’s law. The addition of reagent in a 5 % proportion with respect to the sample is so chosen as to obtain characteristic colors either critical or plateau colors in graphs of color intensit) 2s. volume of added reagent.
-0
5
+o
.I
+I5 0
+ 0 .5 -0.5
2.5 4.5 9.5
-0 5 -1 0 -:i 5 -
14.0
16.5 21.0 25.5
-_ indicate the presence of cracked products (olefins). These are unstable colors and sometimes change noticeably in a few minutes. They are not generally comparable with an S P A scale. In some instances, the observed colors depend on the oil field +here the crude was extracted. This is due to the different ’kinds of aromatics present. In these cases, comparative tests may be of help. In addition, some observed colors depend on the refinement step of the sample. Here also comparative tests imay be useful in making a decision. The precipitation of crystals that sometimes can be obbrrved in the bottom of the tube may provide additional qualitative information. An abundant precipitate when h t i n g naphthas indicates the presence of cracking products.
0
0.0
3 05
35.0
.o
t1.0 0.0 0.0
.
ACCURACY AND PRECISION
The accuracy of this method has been tested with pure hydrocarbon mixtures. Differences are usually under il%, sometimes between & l and 2%, and seldom above &2%. The standard deviation of this method can be estimated withiri
4=0.6%. The precision of this method is within &0.5% whether onlj one operator is working with the same apparatus or several operators with different apparatus. Two or more individual determinationa must not differ from their mean by more than this value. In working with poorly calibrated tubes (with errors of the order of 0.1 ml.) the reproducibility may become only & l . O % . This degree of precision, which is enough for the practical problems of industry, may be increased through: better temperature control, use of tubes with higher capacity and more sensitive graduations, mechanical shaking, centrifugation to separate both layers, and determination of molecular weight with more ac?urate graphs. DISCUSSION OF EXPERIMENTAL RESULTS
This method ww applied as described in nearly 200 tests to samples of the most varied nature including straight-run and cracking naphthas, both light and heavy, belonging to different crudes and having different structures, sulfur contents, and general properties. It was also applied to aviation gasolines, mineral spirits, light and heavy kerosines (refined and unrefined and from
V O L U M E 28, NO. 2, F E B R U A R Y 1 9 5 4 different crudes), jet propulsion fuels, solvents, special cuts, petroleum conversion products (such as samples from hydroforming), several mixtures of the fractions mentioned, and pure hydrocarbons or mixtures of them prepared for the purpose. These samples were also analyzed by the IP (15) and the ASTM methods ( 2 ) . These methods, though often used in the petroleum industry, give only approximate results. The discrepancies between results of the proposed method described here and those of the other two methods have only a relative meaning. A general balance of results, with distribution of errors and differences found, can be seen in Table IV, which includes 90 comparisons with the IP method, 25 comparisons with the ASTM method, and 65 comparisons with pure hydrocarbons. The first.column shows the statistical treatment of the results of this method applied to 22 samples of gasoline, aviation gasoline, and mineral spirits, 11 of which were from cracking. These samples came from crudes from Iran, Peru (HCT), Comodoro Rivadavia (Argentina), and Challaco (Argentina). They were all unrefined fractions with densities varying between 0.7072 and 0.7843 and with the first drop between 35" and 144' C. Their distillation maxima were between 127" and 255' C.; molecular weights were between 90 and 148 and aromatic percentage between 3.0 and 15.2% according to the IP method. The cracking fractions had olefin percentages between 2.3 and 19.6%. The wide range of properties of these 22 samples can b e easily seen. The statistical balance of the first column shows that practically one third of the results are within &0.5% of those obtained with the IP method and 60% of them are within a &LO% limit; none are farther than 3Z2.070. There is a dominance of excess differences with respect to IP method. The cracking products, notwithstanding their olefinic content, showed differences not greater than those cited above. From the qualitative point of view, in straight-run fractions the tests gave either clear, stable yellow, orange, or red colors. I n cracking fractions the colors were either green or brown, dirty and unstable, and crystal precipitation took place. In the second column of Table IV, the statistical results of 25 samples can be seen, 20 of which were kerosines and 5 jet fuels, a11 belonging to petroleums from Iran, Peru (HCT), Challaco (Argentina), Plaza Huincul (Argentina), Salta (Argentina), Mendoza (Argentina), and Comodoro Rivadavia (Argentina). Some were refined and others not, with densities between 0.7892 and 0.8182, first drop between 135' and 179' C., and distillation maxima between 249" and 294" C. The molecular weights were between 150 and 181, and their aromatic contents were between 9.6 and 23.8% according to the IP method. The error distribution indicates that practically half the red t s are within =t0.5% of those obtained with the IP procedure and that 80% of them are within & l . O % and none are farther than &2.0%. Defect differences with respect to the IP method predominate slightly. From the qualitative point of view, clear and stable colors were observed in the yellow, red, and orange hues, characteristic of straight-run products. In certain instances the color was characteristic of the oil field-for instance, red for Iran, orange for Challaco, and yellow for Comodoro Rivadavia. I n the third column of Table IV, the statistical distribution of 20 samples can be seen, 14 of which were jet fuels, 1 was a special cut of very low aromatic content, and 5 were mixtures of different proportions of that cut with jet fuel. The origin of the crude was in all instances Comodoro Rivadavia (Argentina). The ,densities were between 0.7858 and 0.8135, first drop between 15loand205"C.,and distillationmaxima between 263' and286"C. The molecular weights were between 161 and 190. The aromatic content, according to the IP method, was between 2.5 and 11.0% with five samples under 7.0% and 15 samples above 7.0%. The error distribution shows that half the results are within =t0.5Y0of those obtained with the IP method, 75% are
341 within &1.0%, and none are farther than 422.0%. There is a slight dominance of excess errors. In particular, of five samples with less than 7.0% of aromatics, four of them were within &0.5% and the rest with -0.9%, which indicates a fair agreement with the IP method even in the zone of low aromatic content. From the qualitative point of view, the characteristic colors of straight products were observed m always, clear and stable. The samples of low aromatic content were colorless or light yellow. The fourth, fifth, and sixth columns of Table IV show the s t a t i s tical results of Table V involving 10 samples of naphtha, of which three were cracking. The fourth column shows the balance of contrasts against the IP method and the fifth column against the ASTM method (2); the Bixth column shows the balance of differences between these two standard methods. For straight-run fractions there is a reasonable accord with any one of these methods; around 50% of the results agree within =kl.O%. For cracking fractions there are some strong discrepancies that have only a relative meaning, since there are great differences existing between the IP and ASTM methods apart from the fact that they depend on such an approximate and unprecise determination m the bromine number. The seventh, eighth, and ninth columns of Table IV show t h e statistical results of Table VI that involve 16 samples, I1 of which were kerosine, 2 jet fuels, I solvent, and 2 hydroforming samples. The seventh column shows the balance of comparisons with the IP method, the eighth with the ASTM method, and the ninth shows the differences between these two standard. methods. There is a better agreement with the ASTM method (80% of the contrasts within 3Zl.0yo)than with the IP method (only 54% of the contrasts within fl.OOJo). However, comparing the IP method with the ASTM it can be seen that only 58% of the contrasts are within =kl.O%, so the agreement between the proposed method and ASTM is better than between the IP and ASTM methods; the agreement between the proposed method and IP is similar to that of between the IP and ASTM methods. In Tables V and VI many examples can be seen of dilutions with n-heptane and n-hexadecane that illustrate the recommendations for dilution as described above. In the same tables, the repetition of the same analysis using the proposed method and the IP and ASTM methods illustrates the precision of these three methods. In the tenth column of Table IV the statistical results of 65 comparisons of this method with pure hydrocarbon mixtures can be seen, as is detailed in Tables VI1 and VIII. Light and heavy aromatic hydrocarbons were tested, dissolved in varying proportions with normal paraffins Other hydrocarbon families were etudied regarding their capacity to interfere with the picric acid-nitrobenzene absorp tion and also the way to avoid those interferences (dilution). About 90 cases were studied with all the pure hydrocarbons available to this laboratory. Although their number was limited, they were varied enough to make possible the composition of mixtures covering the principal cases and problems in this method, such as variations in differentfamilies of hydrocarbons (paraffinic, isoparaffinic, naphthenic, olefinic, and aromatic), influence of side chains and condensed nuclei, behavior caused by variations in molecular weight, and importance of the relation of the aromatic fraction molecular weight to that of the nonaromatic fraction. In interpreting some of the tests with pure hydrocarbons"3t must be noted that the action of the reagent upon some of t h k when tested individually (Table VII, tests 1 to 12) MXy BE?&normal, in the sense that the absorptions ma$%dk)kx@#d$'"'@k actual aromatic content. However, it is always possible by means of an adequate dilution tM' dBtaiv* ~ ~ $ & t % ~r!v$ sentative of the aromati? , c p a w + r ~ l ~ a ~ ~ f i : : ~ I i ~ ~ ~ The results may also be abnormal when the a r o m & b r c & m t goes beyond cehtdd'liinlt%$ ' %!P%@$: &;B&r& ii&i&~i& be
$fi,A&h
342
ANALYTICAL CHEMISTRY
obtained by means of an adequate dilution to an intermediate aromatic content (Table VII, tests 13 to 19). There is another source of abnormality when the relation between the molecular weight of the aromatics with respect to that of the nonaromatics is too high. In this case absorptions higher than the actual aromatic content may be found (Table VII, tests 46 and 47, and Table VIII, tests 13, 14, and 17). When that relation is too low, absorptions lower than the actual aromatic content may be found (Table VIII, tests 35 to 37). However, there is always a, wide zone of that molecular weight relation in which the results are correct (Table VJI, tests 48 to 53, and Table VIII, tests 1 to 5, 7 to 12, 20 to 25, and 27 to 29). This shows the experimental basis for the recommendation to correct the molecular weight relation by means of an adequate dilution. In the statistical balance of this method with pure hydrocarbon mixtures, covering 65 comparisons, 42 of them (65%) were within an error of 5 0 . 5 % ; 80% of the comparisons were within &l.O% and if one goes as high as &2.0% it is possible to include practically all the samples (95%). These figures become more significant when one realizes that the error covering 50% of the samples is the probable error of a method and the error covering 68.3% of the samples is the mean square error or standard deviation of a method. These must be taken preferably as reasonable limits of error apart from some individual deviations. The standard deviation of this method can be estimated within &0.6%. In the case8 studied the agreement of this method with pure hydrocarbons is better than its agreement with the IP and ASTM methods. This may indicate a better accuracy for the proposed method than for the latter two. ACKNOWLEDGMENT
The author wishes to acknowledge the encouragement of A . J. Zanetta and J. E. Vinai; the careful work of A. Dubin in many comparisons with the IP method; the efficient help of P. EL-Juri and R. Castro; the careful work of C. D. Bizzozero, A. Nieto, and C. Mamberti from Florencio Varela Research Laboratories in the comparisons of this method, especially with the ASTM method; and to thank A. Seoane and 0.
Alonso for drawing the figures; J. E. Simmons for the English version; and S. S. Kurtz, Jr., Sun Oil Co., for his helpful suggestions that contributed to the present form of this paper. LITERATURE CITED
(1) Am. SOC.Testing Materials, Method D 483-40 (1949). (2) Am. Sac. Testing Rlaterials, Tentative Method D 875-46T (1949). (3) Am. SOC.Testing hIateriitls, Tentative Method D 155-451‘ (1949). ( 4 ) Am. Soc. Testing Materials, Tentative Method D 1017-47 (1949). ( 5 ) Bennasar, J., and Rikies, B., “Apuntes sobre Destilacidn del Petroleo,” Val. I, pp. 1634, Buenos Aires, BIP (Yacimientos Petroliferos Fiscales), 1938. (6) Berg, C., and Parker, F. D., ANAL.CHEM., 20,456‘(1948). (7) Conrad, A. L.,Ibid., 20,725 (1948). ( 8 ) Cosciug, Timothei, Petroleum Z . , 31,5-7 (1935). (9)Ellis, C., “The Chemistry of Petroleum Derivatives,” 1’01. 11, p. 30,New York, Reinhold Publishing Corp., 1937. (10)Ibid.. D. 1155. (11) Gambkll, C. M., and Martin, K. B., IXD.ENG.CHEM.,ANAL. ED.,18,689(1946). (12)Godlewicz, M., Nature, 764,1132 (1949). (13) Heigl, J., Black, J., and Dudenboatel, B., ANAL.CHEM.,21, 554 (1949). (14) Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds,” pp. 496-519, New York, John Wiley &Sons, 1941. (15) Institute of Petroleum (London), Method IP 3/42 (1946). (16) Jones, H. O., and Wootton, H. A,, J. Chem. Soc., 91, 1146 (1907). (17) Lipkin, ‘M, R., Hoffecker, W. A., Martin, C. C., and Ledley, R. E., ANAL.CHEM.,20,130(1948). (18) Mills, I. W., Kurtr, S. S., Jr., Heyn, H. A., and Lipkin, M. R., Ibid., 20,333 (1948). (19) Sachanen, A. N., “The Chemical Constituents of Petroleum,” p. 136,New York, Reinhold Publishing Corp., 1945. (20)Ibid.. DD. 155-6. (21) SpakoGsky, A. E.,Evans, A,, and Hibbard, R. R., ANAL. CEEM.,22,1419 (1950). (22) Watson, K.,and Nel~on,E. F., I d . Eng. Chem., 25, 880 (1933).
RECEIVED for review April 3, 1952. Accepted July 31, 1953. Presented E t the First South American Petroleum Meeting, Montevideo, Uruguay, Msroh, 1951.
Pyrohydrolysis in the Determination of Fluoride and Other Halides JAMES C. WARF’, W. D. CLINE*, and RUTH D. TEVEBAUGH3 institute for Atomic Research and Department of Chemistry, lowa State College, Amos, lowa
T
H E preparation of large quantities of uranium( IV) fluoride and thorium fluoride by hydrofluorination of the oxides, in the Manhattan Project during the years 1942-1945, necessitated a rapid and accurate analytical method for determining these and other halides. Various modifications of the fluosilicic acid distillation technique of Willard and Winter ( 2 3 )were in use, but these were time consuming, especially with fluorides produced a t high temperature, and other methods ( 1 2 ) were not promising. A method based on reversal of the preparative reaction of the &yorides was developed, and proved highly satisfactory and versa,#&3 $he method consisted essentially of passing a current of f g ~ r@e fluoride in a platinum apparatus at a high tem.~r&~~KJ~&py& condensation ,by and titration of the hydro-
--
fluoric acid produced. An abstract of the method was published in the National Nuclear Energy Series (21) based on the original project literature (22). Industrial High-Temperature Hydrolyses. The early literature records a wide variety of hydrolytic experiments a t elevated temperatures, most of which were concerned with industrial production of hydrochloric acid. In 1809 Gay-Lussac and Thenard (11 ) first proposed the manufacture of hydrochloric acid and sodium silicate from salt, sand, and steam. Pelouze ( 1 3 ) suggested the use of calcium chloride and steam, while Solvay (18) attempted to accelerate the hydrolysis of calcium chloride through addition of siliceous materials. Iler and Tauch (8) examined a score of proposed methods for commercial production of hydrochloric acid via hydrolysis of salt-sand mixtures and attempted to operate the three most practicable variations on a laboratory scale. Low yields, owing to an unfavorable equilibrium constant, and high heat loss, owing to vaporization of sodium chloride, precluded industrial succesa.
