September, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
I n conclusion, it is evident that we now have available alkyd resins with definite and controlled flexibility. This has been accomplished in a new manner, not by adding external plasticizers and flexing agents, but actually by introducing these properties into the resin molecule through intentional formulation I
LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8)
Callahan, M. J., U. S. Patent 1,091,732 (Mar 31, 1914). Carothers, W. H., Chem. Rev., 8, 3 5 3 4 2 6 (1931). Carothers, W. €I,, J . Am. Chem. Soc., 51, 509 1:1929). Carothers, W. €I., and Awin, J. A,, Ibid., 51, 2560 (1929). Carothers, W. H., and Dorough, G. L., Ibid., 52, 711 (1930). Carothers, W. H., and Hill, J. W., Zbid., 54, 1579 (1932). Kienle, R. H., IWD. ENQ.CKEY.,22, 590 (1930:i. Kienle, R. H., and Ferguson, C. S., Ibid., 21, 349 (1929).
915
(9) Kienle, R. H., and Hovey, A. G., J. Am. Chem. Soc., 51, 509 (1929). (10) Ibid., 52, 3636 (1930). (11) Kienle, R. H . , and Rohlfs, H. C., U. S. Patent 1,897,260 (Feb. 14, 1933). (12) Meyer, K. H., and Mark, H., Ber., 61, 593 (1928). (13) Pickles, S. S., J . Chem. Soc., 98, 1085 (1910). (14) Staudinger, H., “Die hochmolekularen organischen Verbindungen,” Springer, 1932. (15) Staudinger, H., Brunner, M., Frey, K., Garbsch, P., Signer, R.. and Wehrli, S., Ber., 62, 241 (1929). (16) Whitby, G. S., McNalley, J. S., and Gallay, W., Trans. Rou. Soc. Canada, 22, 27 (1928). (17) Wright. J. G. E., Chem. & M e t . Eng.,39, 438 (1932).
RECEIVED April 28, 1933. Presented before the Division of Paint and Varnish Chemistry a t the 85th Meeting of the American Chemical Society, Washington, D. C., March 26 to 31, 1933.
Pressure-Temperature and Low Pressure Total Heat Relationships of Petroleum Fractions E. G. RAGATZ, 13. R. MCCARTNEY, AND R. E. HAYLETT, Union Oil Company of California, Los Angeles, Calif. A method of identifying the equivalent pure tween the dew line and the boilN A N EFFORT to develop a cut of a wide-cut fraction has been developed, ing Point line is the boiling range method for predicting the of the distillate for that particudew and lines for and data have been analyzed to show that the lar pressure, and points between petroleum fractions, vapor prescritical Point for such a cut constitutes the cornthe dew and boiling lines indicate sure charts have been devised by mon point of convergence f o r the dew lines of all various c o n d i t i o n s of partial various investigators from the d a t a of t h e p u r e compounds, similar wide-cut fractions of equal gravity. vaporization. The differencein This equivalent pure-cut critical point can also the spread of these two loops is particularly the pure paraffins. brought about entirely by the The common aim of these inbe used as a guide for the development of wide-cut differencein boiling range, since vestigators has been to produce boiling lines and partial vaporization effects. the two cuts were of the same a chart on which the vapor presFinally, the equivalent pure cut can be used as A. P. I. gravity and molecular sures of the pure compounds plot a basis for calculating the total heats of lowweight, and hence, for thermal as straight lines converging a t a single p o i n t . The coordinate pressure petroleum fraction vapors. purposes, of the same composition. system described by Maxwell (5) accomplishes this purpose reEQUIVALENT PURECUTS markably well; hence it has been used in the following discussion. When the observed boiling and dew points of the two While a family of radiating straight lines drawn on such a Bahlke and Kay fractions were plotted against boiling range chart as Maxwell’s represents the pure compound data within for several different pressures, as in Figure 2, and straight engineering accuracy, large errors may occur when these lines drawn through the respective points, the straight lines pure-cut lines are used for estimating the dew and boiling were found to intersect on the ordinate for zero boiling range, lines for petroleum mixtures, since the lines for such mixtures thus defining a series of boiling points for a hypothetical cut across the pure-compound lines a t various angles, de- hydrocarbon of zero boiling range. Furthermore, when pending on the width of the cut (Le., its boiling range). these hypothetical boiling points were, in turn, plotted on Consequently, some method of evaluating the changes of the vapor pressure chart of Figure 1, they were found to fall slope of the wide-cut lines must be developed before a vapor exactly along a pure-compound line; that is, they fell on a pressure chart for a pure compound can be accurately applied straight line which, when extended beyond the range of the to wide-cut petroleum fractions. chart, passed through the common point of convergence for A method of attacking this problem was suggested by all other pure-hydrocarbon vapor pressure lines. But the Bahlke and Kay’s study (2) of the thermal properties of hypothetical pure cut represented by such a line would have two petroleum distillates which differed only in boiling range. the same gravity and molecular weight as the two actual The heavy loops on Figure 1 are plots of Bahlke and Kay’s cuts from which it was derived; consequently, this zero vapor pressure data for these two distillates. The upper, boiling range cut could be considered as the equivalent pure dashed line of each loop is the dew line-that is, the line of cut of the actual wide-cut fractions. Such an equivalent complete vaporization or initial condensation for the cut in pure cut furnishes a basis for the measurement of the effect question-while the lower, solid line is its vapor pressure of boiling range on the slope of the dew and boiling point line, or line of initial vaporization, or complete condensation. curves of a wide-cut fraction, since all wide-cut fractions of At any given pressure, the indicated temperature gap be- the same gravity and molecular weight can be considered
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INDUSTRIAL AND E K G I S E E R I N G
CHEMISTRY
Vol. 25, No. 9
The required dew point data may be readily determined in the laboratory by the aid of the continuous dew point still shown in Figures 3 and 4. This still has been reduced to a piece of routine laboratory apparatus by means of which dew points can be easily obtained by the ordinary operator. By suitably controlling its heating and rate of feed, the amount of liquid retained in such a still can be held constant, and the overhead distillaLL: I 400--tion rate m a i n t a i n e d e q u a l to the feed rate. W Hence, as distillation proceeds, the composition a: of the retained liquid will change until it reaches 3 3 0 0 -equilibrium with the vaporized feed m a t e r i a l . After this equilibrium has been a t t a i n e d , the composition of the incoming feed and outgoing a 200 -vapors will be the same, and the vapor outlet 2 W thermometer will record the dew Doint of the feed !material a t the still pressure. This dew point still is readily operable a t absoloo -lute pressures down to 100 mm. For critical intersection calculations, laboratory dew points should be obtained on the desired wide-cut fractions for a series of pressures ranging from 100 to 760 mm. 32 0.5 500 io00 After obtaining the necessary laboratory dew point data, the critical intersection and equivaFIGURE 1. VAPORPRESSURE CHART lent pure-cut values for the wide-cut f r a c t i o n can be graphically determined as indicated on as having been derived from a single equivalent pure cut by Figure 5, where the method has been applied to a Los Angeles the spreading out of their dew and boiling lines through Basin cut. For this graphical solution, the laboratory dew point data fractional blending. are plotted on a hlaxwell vapor pressure chart, and a straight CRITICALIXTERSECTIOSS line is drawn through these points and extrapolated out into I n order to make use of this conception of a hypothetical the critical region. It has already been noted that the critical pure cut, it was necessary to find some property common to intersection for a wide-cut fraction is practically identical this cut and to all the wide cuts derived from it, which would with the critical point of an equivalent pure cut which has the not be affected by boiling range. Three cuts as closely re- same gravity as the wide-cut fraction. Consequently, the lated as Bahlke and Kay’s two actual cuts and their equiva- solution of the critical intersection problem involves the lent pure cut could well be expected to have a t least one identification of a hypothetical pure cut having a gravity point in common in the pressure-temperature plane. The equal to the wide-cut gravity, and dew lines of the two Bahlke and Kay cuts almost intersect a vapor pressure curve which ina t one point on Figure 1 (595’ F. and 435 pounds per square tersects the wide-cut dew point line inch absolute) ; and in confirmation of the above supposi- a t the critical temperature of the s tion, the point of closest approach of these two dew lines pure cut. E a t o n a n d P o r t e r ( 3 ) h a v e k4” was found to lie close to the critical point of the equivalent pure cut (located by methods described later). This led r e c e n t 1y published a relationship to the hypothesis that, within engineering accuracy, the between gravity, atmospheric boilcritical point of an equivalent pure cut can be taken as com- ing point, and critical temperature mon to the dew lines of all corresponding fractions of equal for pure hydrocarbons. This relagravity, regardless of width of cut. For brevity, such points tionship (which is expressed by the BOILINORANGE- 7 curve of Figure 6 with the excephave been called “critical intersections.” The value of this concept of a critical intersection lies in tion that the extrapolated high- F I G U R E 2. E X T R A W the fact that it extends the range of usefulness of the vapor temperature section has been drawn ;::pFO pressure chart to include the wide-cut type of fraction nor- in somewhat higher than indicated B~~~~~ A N D K ~ mally encountered in petroleum refining practice. The above by Eaton and Porter) can be used FRACTIONSTO ZERO BOILINGRANGE described critical intersection points appear to bear the same for identifying the desired pure-cut relation to the dew lines of wide-cut fractions that the com- curve. In applying Eaton and Porter’s data, two pure-cut dew mon point of convergence bears to the dew lines of pure compounds; although a different set of critical intersection lines (i. e., straight lines passing through the pure compound points will be required for the cuts from each given crude convergent of Figure 1) are drawn in such positions that one source, whereas the common convergent for the pure com- passes somewhat above, and the other somewhat below, the extrapolated wide-cut dew line in the critical region. Critical pounds remains fixed for all classes of hydrocarbons. temperatures are then calculated for these two assumed cuts, LOC-ATION OF CRITICALINTERSECTIONS BY THE AID OF using the atmospheric dew points indicated by the respective LABORATORY DATA pure-cut intersections with the atmospheric pressure ordinate, The critical intersection point for a fraction cut from any together with the observed gravity of the wide-cut fraction, given type of crude can be identified by gravity alone. for entering the critical temperature plot of Figure 6. These Such an identification, however, requires a preliminary labo- calculations will give the critical points A-A of Figure 5. ratory determination of the gravity-dew point relationships But the critical point for the true equivalent pure cut must fall exactly on the extrapolated wide-cut dew line; hence, if of a series of fractions cut from the crude in question. 1200-
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for d l s i l c l i c i i r v e s a n e t w o r k of gravity- inolccular weight codrdinates in the critical rcgion. l f this were
tile two assunred p u r e - c u t curves h v e been drawn fairly close t,, t,he w i d e - c o t d e w line, a iihraiglit. line drawn between point.s A-A will cross the vide-cut dew line at the desired critical int.erseetion, and a pure-cut, line drawn t h r o u g h this point will define the equivalent pure cut of the ' ion. wide-cut. fract'
tioii being t h e n l o c a t e d froiir t h e gravity and narlecular weight of the fract,ion alone, without referencc to its source or coinposition. An attempt to d e v e l o p such a gravitymr,lecular weight ciriirdinate system ! a s not becn entirely successful; Imvevcr, the relationstrips so fa,r developed are suificicntly siiggestive to warrant their inclusion in this dis-
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