I N D U S T R I A L A N D ENGINEERING CHEMISTRY
November, 1924
1131
A Boiling Point Correction Chart for Normal Liquids' With Special Application to Petroleum Products By W. H. Bahlke and Robert E. Wilson STANDARD OIL Co. (INDIANA), WHITING, IND.
9 THE specifications
a c c: u r a t e vapor pressure From accurate vapor pressure curvesf o r the normal parafin hydroadapted by the Federal curves for the paraffin hycarbons a chart has been prepared covering the boiling point correcSpecifications B o a r d drocarbons,* and their aptions to be applied when the pressure at which the distillation takes on February 3, 1923, is a plicability to petroleum place is diyerent f r o m that at which it is desired to know the boiling table of corrections to be products is justified by temperature. This chart m a y be used with quite reasonable accuracy applied to the observed data in the later sections. f o r any of the so-called normal or nonassociated liquids, and boiling temperature in a The exact procedure was should be valuable in the petroleum industry f o r correcting the boildistillation test whenever as follows: On a large-scale ing temperatures observed in the A . S. T . M . Engler distillation the barometric pressure a t plot of the log of the vapor method, when the barometric pressure during the test is considerably which the test is made is pressure against the log of different f r o m that at the point of consumption. The existing cordifferent by more than 25 the absolute temperature, rection table2 a .m.x a r s to be considerablu i n errcr. mm. from the average barothe slopes of the c;rves for metric pressure at the point t h e c o m p o u n d s from nof consumption. This table, however, does not cover tem- pentane to n-tetracosane, inclusive, were measured a t the peratures above 690' F., and it was desired to correct the point midway between 600 and 760-mm. pressure. The distilla tion temperatures of products that boil somewhat slopes thus obtained were then plotted against the temperahigher than this. Since no extensive data appeared to be ture (' F.) of the normal boiling point in order to minimize the available, it seemed desirable to calculate the corrections by errors in reading slopes. a reliable method and test the accuracy of the method at The resultant data are plotted in Fig. 1, with the most reptemperatures where the data are available. resentative line drawn through the points. Inspection of the vapor pressure curves will show that the slope is very CONSTRUCTION O F CHART nearly constant between 600 mm. and 760 mm., so that the The validity of a method for correcting boiling points based assumption that the curves are straight between these two rigidly upon accurate vapor pressure observations cannot be points would introduce no large error. This assumption was questioned, and since Hildebrand has shown the remarkable therefore made, and the corrections given graphically in Fig. 2 similarity between the vapor pressure curves of all normal were calculated from the slopes given by the line in Fig. 1. liquids, at similar values of p / T , it is possible to give, in graphiDISCCSSION OF RESULTS cal form, precise boiling point corrections which should apply There is one equation that is frequently used in correcting to all normal (nonassociated) liquids under consideration. It mould be expected also that the same corrections would boiling points from observed to normal pressure-namely, apply to any mixture of liquids which obeys Raoult's law. the equation of Young:& From 1he data of Wilson and Wylde3 it appears that a mixe = ~ ( 7 6 0- P ) (273 t ) (1) where 0 = correction to be applied ( " C.) ture of petroleum hydrocarbons with molecular weights of a C = constant = 0.00012 similar order of magnitude would obey Raoult's law and thereP = observed pressure fore that the correctionsfound for pure hydrocarbonswouldalso t = observed boiling temperature ( " C.)
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INDUSTRIAL AND ENGINEERING CHEMISTR Y
1132
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at the normal boiling point where the term - is apw v - vz proximately constant for all substances.6 The equation can,
Vol. 16, No. 11
run both a t Casper, Wyo., and Whiting, Ind., on twenty-nine samples of Solite gasoline. The average barometric pressure a t Casper was about 635 mm., while a t Whiting it was 750 mm. From these results it appears that the corrections given in the Bureau of Mines table are entirely too high-in fact, the corrections are nearly twice those given by either of the other methods and more than twice those observed.’ As far as these observations are concerned, they appear to check the Young equation results more closely than they do the proposed chart, though the differences are not large enough to be very significant in view of the variations in individual results. TABLE I-DISTILLATIONOF SOLITE(HIOR TEST) GASOLINE$ e-----
Points on distillation curve Per cent Initial 10 t o 40 50 t o 90 Maximum
PIG.2
therefore, be no more accurate than the constancy of the In fact, the constant in Equation 1 determ -.
w v - vi
termined by Young from the tangents to the vapor pressure curves at the normal boiling point has the following values for the normal paraffin hydrocarbons: methane 0.000135, pentane 0.000125, hexane 0.000122, heptane 0.000121, octane 0.000119. I n view of this decrease of the “constant” with increasing molecular weight, the equation is probably less accurate, especially for the higher hydrocarbons, than
Temperature range
OF.
8 5 t 0 100 145to230 235 t o 330 385 to, 395
Average observed 5.4 7.3 9.0 10.8
CORRECTION O F. From chart 9.2 9.5 10.9 12.4
From From Young’s B. of M . equation table 7.5 13.8 8.9 16.1 18.4 10.2 11.7 21.2
I n order to test the reliability of the vapor pressure curves over a much wider range of pressures, the calculated corrections obtained from the curves are compared in Table I1 with the observed corrections obtained from distillations of the same sample of Red Crown gasoline a t 760, 505, and 310 mm.* These distillations are plotted in Fig. 3. As was the case at higher pressures, the vapor pressure curves give results that check very well with the observed corrections. Since the constant in Young’s equation was obtained from the slope a t the normal boiling point of the curve of vapor pressure against temperature, the equation is necessarily considerably in error a t these low pressures for which it was not intended. TABLE11-DISTILLATIONO F RED CROWN GASOLINE ----CORRECTION ( ” FJ-From vaPressure por pres- From Young’s Mm. Hg. Observed sure curves equation 505 29 24 20 810 53 50 34 505 27 25 21 310 55 53 36 505 26 26 23 310 55 56 38 505 22 27 24 310 50 57 42
Points on distillation curve Per cent 26 46 71 91
I n view of these results it is believed that the table given by the Federal Specifications Board should be supplanted by the chart given in this paper or by a table based on the Young equation and that the proper steps should be taken to have it officially adopted. 7Correspondence with the bureau has developed the fact t h a t t h e corrections were based upon a limited number of distillations a t two points of different altitude, combined with figures calculated from the Young equation. However, in some way the proper corrections from the equation were erroneously multiplied by 1.8. I n view of this fact and t h e experimental results presented in this paper, t h e bureau plans further work in t h e near future t o settle this point. 8 Run by R. N. Jarman of this laboratory.
FIG.
3-DISTlLLATIONS
OF
RZDC R O W N GASOLINE
the method used in constructing the chart given in this paper. Another fact making for greater accuracy in the recommended chart is that the log-Iog curves have more nearly a constant slope between 600 and 770-mm. pressure than do the ordinary vapor pressure-temperature curves. A comparison of the corrections obtained by the various methods is given in Tables I and 11. In the column headed “observed” in Table I are the average results of distillations Despretz, Ann. chkm. phys., 24, 323 (1823); Ramsay, Address, Philosophical Society, Glasgow, 1877 ; Trouton, Phil. Mag.. 18, 54 (1884).
Chemical L a b o r a t o r y Gift Bishop Lawrence, chairman of the committee to extend the national service of Harvard University, has announced a gift of $475,000 for the division of chemistry, from the family of t h e late E. C. Converse of New York, one of the most prominent of the group of international financiers who founded the United States Steel Corporation. I n mentioning the gift Bishop Lawrence said: The family of t h e late E. C. Converse of New York has given $475,000 to be used for the erection of a chemical research laboratory a t Harvard as a memorial t o Mr. Converse and t o carry his name. The members of t h e family who have contributed this gift are Mrs. E. C. Converse, his daughters Mrs. Benjamin Strong and Mme. Antoinette Converse, and his son E. C. Converse.
