Phase Equilibria in Hydrocarbon Systems Methane-n-Butane-Decane System H. H. REAMER, B. H. SAGE,
AND
W. N. U C E Y
California Institute of Technology, Pasadena, Calif.
square inch for temperatures between 100" and 460" F., but the data are not yet published. The comhsition of the dew-point gas in the methane-decane system was determined a t loo", 160", and 220"F. for pressures below 2500 pounds per square inch absolute by Lavender, Sage, and Lacey (4). They also published results from a volumetric study of this system at pressures below 4500 pounds per square inch for temperatures between 70" and 250" F. (14). The authors' laboratory has reported an extension of the data for this system to 10,000 pounds per square inch and 460"F. (8). As a part of the present investigation the volumetric behavior of the liquid phase of the n-butane-decane system was determined at pressures from bubble point to 10,000 pounds per square inch absolute for temperatures from 100' to 460" F. The results have not yet been published. These various investigations served to establish the volumetric behavior of the binary systems bounding the ternary methanen-butane-decane system throughout wide ranges of pressure and temperature, including the single-component apices of the ternary composition diagram shown in Figure 1. This paper is the first of a series which will undertake to describe the volumetric and phase behavior of three-component mixtures whose compositions may be represented by points distributed systematically over the interior of the ternary diagram. The group of mixtures considered in this paper lies along a straight line cutting across the ternary composition diagram from the methane apex to a point on the n-butane-decane boundary corresponding to 0.66 mole fraction n-butane (Figure 1). The compositions of the mixtures experimentally studied are indicated along the line.
Five mixtures of the ternary system consisting of methane, n-butane, and decane were studied volumetrically at seven temperatures from 100" to 460" F. and at pressures up to 10,000 pounds per square inch absolute. The mixtures were chosen 80 as to have a fixed molal ratio of nbutane to decane of about 2 to 1, whereas the mole fraction of methane varied from 0.3785 to 0.9775. The experimental results establish the volumetric properties of these mixtures in the single-phase region, at pressures above that of the bubble point and, in the two-phase region, near the bubble-point boundary.
T
HE volumetric and phase behavior of single-oomponent and binary systems involving the lighter aliphatic hydrocarbons have been studied by many investigators and much information concerning these systems has been published. To a lesser extent the equilibrium distribution of components between coexisting fluid phases of ternary hydrocarbon systems has been studied. However, little information is available concerning the pressurevolume-temperature properties of ternary systems. Such information would provide an opportunity to compare the partial volumetric behavior of each of the components in the ternary system with that found in the related binary systems (10, l a ) . Such a comparison would aid greatly in attempts to predict quantitatively the volumetric and thermodynamic properties of multicomponent hydrocarbon systems. For these reasons an experimental investigation was undertaken to establish the volumetric and phase behavior of the methane%-butane-decane system a t pressures up to 10,000 pounds per square inch absolute and a t temperatures between 100" and 460 ' F. A number of investigations have established the properties of methane and n-butane in the pure state, and good agreement between investigators (6, 7) was attained. The specific volume of liquid n-decane and its boiling point at atmospheric pressure were determined by Shepard, Henne, and Midgley (15),and the vapor pressure at two temperatures was reported by Young (16). Sage, Lavender, and Lacey (14) measured the specific volume of liquid decane at pressures up to 3500 pounds per square inch for temperatures between 70" and 250' F. The authors have extended these measurements to 10,000pounds per square inch and 460 " F.
MATERIALS
Gas from the Bowerbank Field in the San Joaquin Valley, Calif., was used as the source of methane. The gas consisted primarily of methane and water vapor with traces of carbon dioxide. Before being introduced into the pressure-volume-temperature apparatus the gas, a t a pressure above 1000 pounds per square inch absolute, was passed through a chamber packed with successive layers of granular calcium chloride, activated charcoal, potassium hydroxide, and anhydrous calcium gulfate. The purity of a sample of gas treated in this manner wa [tested by methods involving partial condensation at liquid air temperatures, gas density determination a t atmospheric pressure, and Orsat analysis of reaction products resulting from combustion with pure oxygen. These tests indicated that the quantity of hydrocarbons less volatile than methane was less than 0.02 mole % ' and the amount of noncondensable gases was less than 0.1 mole %. Butane was obtained from the Phillips Petroleum Company, the accompanying analysis indicating the presence of less thaq 0.3 mole % isobutane and negligible amounts of other impurities. This material was distilled with a reflux ratio of about 50 to 1 in a fractionating column four feet long packed with broken glass helices. The initial tenth and the final fifth of the charge in the distillation column were discarded, and the middle fraction was
(8).
The properties of coexisting phases in the methane-n-butane system, at temperatures from 70" to 305.6"F., the critical temperature of n-butane, were reported by Sage, Hicks, and Lacey (11), and the volumetric and partial volumetric properties of this system throughout the single-phase region a t pressures up to 3000 pounds per square inch absolute for temperatures between 70 " and 260' F. were described by Sage, Budenholzer, and Lacey (9). Beattie, Stockmayer, and Ingersoll (1) reported single-phase volumetric studies of three mixtures of methane and n-butane a t pressures up to 5OOO pounds per square inch for temperatures from 167" to 572" F. The studies of this system at the authors' laboratory have recently been extended to 10,000 pounds per 77
.
78
Vol. 39, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY METHOD
Figure 1.
~
Ternary Composition Diagram Showing Series of Mixtures Studied
condensed a t liquid air temperature with continuous removal of any noncondensable gases which may have been present by means of a mercury vapor diffusion pump. A sample obtained by this process showed a difference of less than 0.25% in its vapor pressure a t 280' F. when 57, and when 50% of the sample was in the gas phase. The decane used in this study was obtained from the Eastman Kodak Company and was distilled a t reduced pressure to remove dissolved gas and possibly to improve its purity. The resulting material had a specific volume of 0.022316 cubic foot per pound a t 100" F. and atmospheric pressure (1.3931 ml. per gram a t 37.8' C.) and a refractive index of 1.4100 at 77' F. measured for the D line of the sodium sphctrum. These data, compared with available information concerning the properties of n-decane (16) and of several decane isomers (3, 6), indicate that the material used in this work was composed primarily of paraffin hydrocarbons consisting of ten carbon atoms per molecule but that it probably 'was not entirely n-decane.
No important modifications in the equipment and procedures already described (13) were necessary for the present investigation. The volumetric apparatus consisted of a stainless steel chamber, called the equilibrium cell, whose effective volume could be varied bqthe injection or withdrawal of mercury. The volume occupied by the hydrocarbon sample was known in terms of measurements of the position of the mercury surface in an adjoining interconnected pressure vessel, which served as a reservoir for mercury injected into or withdrawn from the equilibrium cell; suitable corrections were made for the effects of pressure and temperature upon the volumes of the equilibrium cell and of the mercury. The temperature of the oil bath surrounding this cell was controlled by an electrical thermostat and was determined by use of a platinum resistance thermometer whose resistance was measured with a Mueller bridge. Over a period of a number of years the resistance thermometer had been checked several times by comparison with a similar instrument manufactured by Leeds and Xorthrup and certified by the National Bureau of Standards, and no appreciable change in its calibration was noted. The pressure in the cell was transmitted hydraulically through the mercury injection system to a piston-and-cylinder fluid pressure balance. The pressure balance was calibrated a t approximately semiannual intervals by comparison with the vapor pressure of pure carbon dioxide at 0 ' C., using Bridgeman's value of 506.56 pounds per square inch absolute as a standard ( 2 ) . Over a period of two years the calibration of the pressure balance changed only 0.2%. The mixtures of the three components were prepared in the cell. The decane was measured volumetrically in the liquid state with a calibrated glass buret. Next n-butane was added in slight excess from a small steel sample bomb, t l e amount being determined from the difference in weighings on an analytical balance. A small, accurately measured volume of the gas phase of the n-butane-decane mixture was withdrawn from the cell under known conditions in order to adjust the ratio of n-butane to decane of the cell contents more closely to the desired value. After this adjustment, methane was added from an isothermal, isochoric reservoir in which the gas was stored at somewhat higher
0.9
08
07
06
I 1000
I 2000 PRESSURE
I
3000 L B /sa
I
4000
IN
I
1.21
2000
I
4000 PRESSURE
Figure 2. Relation between Compressibility Factor and Pressure for Mixture Containing 0.5763 Mole Fraction Methane
6000
1
1
8000
Ls./sa. I N
Figure 3. Effect of Pressure on JIolal Volume for Mixture Containing 0.5763 Mole Fraction Methane
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1941
TABLEI. Pressure Lb./Sh. In. Abs.
...
B.P. 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3500 4000 4500 5000 6000 7000 8000 9000
10,000
... R.P.
800 1000 1250 1500 1750 2000 2260 2500 2750 3000 3500 4000 4500 5000 6000 7000 8000 9000 10,000
...
.B.P.
200 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3500 4000 4500 5000
6000 7000 8000 9000 10,000
looo F.
hfOLAL VOLUMES FOR MIXTURES OF &THANE,
160' F. 220' F. 280' F. 340' F. 400' F. 460' F.
MOLEFRACTION METHANE= 0.3785, C = (1400) d (1605) (1761) (1850) (1848) 1.6814 1.7921 1.9319 2.1283 2.4274 7.410 5.841 ... 4.650 3.783 5 .??5 7 1 ' 99 ' 3.426 2.816 4.163 5.085 6 '166 2.2614 2.739 3.285 3.940 4.720 3.102 1.8462 2.2175 2.620 3.654 3.000 1.6755 1.8932 2,2170 2.582 1.6688 1.7830 1.9424 2,2359 2,562 1.6602 1.7686 1.9087 2.0962 2.3615 1.6525 1.7548 1.8866 2.0543 2.2806 1.6440 1.7422 1.8662 2.0201 2.2196 1.6374 1.7309 1.8476 1.9914 2,. 1710 1,6300 1.7207 1.8315 1.9668 2.1303 1.6170 1.7021 1,8039 1.9243 2.0632 1.6051 1.6853 1.7800 1.8896 2.0111 1.5940 1.6710 1,7590 1.8596 1.9692 1.5835 1.6566 1.7395 1.8339 1.9357 1.5644 1.6320 1.7069 1,7905 1.8800 1.5476 1.6105 1.6793 1.7554 1.8357 1.5333 1.5930 1.6560 1,7255 1.7991 1.5206 1.5775 1.6353 1,6997 1.7656 1.5092 1.5626 1.6170 1.6755 1.7344
0.6617 (1695) 3.034
MOLEFRACTION METHAKE= 0.5763, C = (2400) (2641) (2726) (2657) (2432) 1.4666 1.5892 1.7631 2.0227 2.4522 4.160 4.991 ... 4.660 3 , 2 7 8 3.932 3.118 2.600 4.274 3.672 2.1684 2.602 3.049 3.529 4.028 1.8802 2.2452 2.620 3.016 3.425 1.6785 1.9888 2.3087 2.643 2.984 1.5331 1 , 7 9 9 8 2.0745 2.3607 2,650 1.4698 1.6554 1.8936 2.1402 2.4058 1.4433 1.5800 1.7595 1.9912 2.2692 1.4304 1.5586 1.7198 1.9224 2.1635 1.4100 1.5232 1.6605 1.8245 2.0105 1.3932 1.4952 1.6150 1.7552 1.9113 1.3785 1.4717 I . 5797 1.7028 1.8401 1.3655 1.4515 1.5498 1.6614 1.7845 1.3431 1.4180 1,5034 1.5962 1.6986 1.3235 1.3904 1.4671 1.5466 1.6339 1.3064 1.3676 1,4364 1.5076 1.5834 1.2903 1.3482 1.4111 1.4750 1.5429 1.2766 1.3302 1.3881 1.4469 1.5085
0.6617 (2045) 3.263
.
.
...
...
...
... ...
5,660 4.302 3.480 2.967 2.734 2.587 2.4837 2,4046 2.3405 2.2393 2.1627 2.1022 2.0543 1,9788 1.9201 1.8746 1,8362 1.8003
6 .i i 7 5.004 4.074 3.539 3.203 2.967 2.802 2.672 2.575 2,4334 2.3292 2.2483 2.1842 2.0878 2.0153 1.9584 1.9129 1.8710
... ... ... ... ... 4 . 369 3.834 3.446 3.154 2.932 2.757 2.4951 2.3098 2.1773 2.0781 1.9324 1.8314 1.7565 1.6973 1.6458
MOLEFRACTION METHAKE= 0.8042, C = 0.6641 (3480) (3560) (3475) (3185) (2670) ... 1.3225 1.5066 1.7513 2.1310 2.813 ..* ... ... 45.36 22.262 ... ... .14.614 10.816 4 . sb'4 8.555 3.518 4 .'is9 4 ,s i 5 6.770 2.882 3.445 4.536 5.069 5.600 3.997 2.4407 2.929 4.316 4.780 3.402 3.866 2.1227 2.553 2.966 3.371 3.762 4.182 1.8876 2.2697 2.634 3.719 2 , 9 9 3 3.338 1.7130 2.0502 2.3747 2.696 3.003 3.362 1.5790 1.8766 2.1671 2.4542 2.741 3.078 1.4736 1.7399 1.9986 2.2566 2.544 2.849 1.3200 1.5275 1.7433 1.9877 2.2450 2.503 1.2629 1.4269 1.6124 1.8126 2.0372 2.2558 1.2232 1.3633 1.5234 1.6951 1.8850 2.0738 1.1924 1.3149 1.4556 1.6070 1.7677 1.9370 1.1449 1.2435 1,3552 1.4776 1 6034 1.7400 1.1118 1.1939 1.2862 1.3857 1.4914 1.6016 1.0843 1.1557 1.2360 1.3211 1.4098 1 5042 1.0595 1.1246 1.1960 1.2722 1.3474 1.4287 1.0371 1.0989 1.1625 1.2282 1.2969 1.3689
48.8i 24.172 15.960 11.867 9.418 7.477 6.193 5.289 4.619 4.114 3.719 3.404 3.147 2.750 2.4626 2.2567 2.1013 1.8737 1.7176 1.5992 1.5126 1.4454
... ...
...
... ...
...
... ..*
.. . ... ... ... ...
3
MOLEFRAOTION METHAKE= 0.9096, C = 0.6598
4.560 3.859 3.342 3.002 2.766 2.587 2.4461 2.2443 2.1029 2.0023 1.9246 1.8112 1,7290 1.6660 1.6169 1.5765
... ... ...
DECANE I N CUBIC FEET PER P O U N D MOLE
Pressure Lb./&. In. Abs. 100' F. 160' F. 220' F. 280' F. 340' F. 400' F. 460' F.
(1357) 4.517
...
... ...
n-BUTAxE, AND
79
...
pressure than was needed for direct transfer to the apparatus. This reservoir was calibrated in terms of pressure readings by systematic withdrawal of methane in amounts which were determined gravimetrically. The study of the pressure-volume-temperature properties of a ternary system throughout the entire range of possible compositions for extended intervals of pressure and temperature is an undertaking of a magnitude far exceeding that of the corresponding study of a binary system. The specification of the composition of a ternary system requires the assignment of values to two parameters relating to the relative amounts of the three components, whereas in a binary system only one such parameter need be fixed. The graphical treatment of the results is greatly facilitated if the experimental observations are confined t o equilibrium states of the system in which variation is permitted only in two variables, all others being held a t known values. It was convenient to
MOLEFRACTION METHAKE= 0.9775, C = 0.6598
a Figures in parentheses represent bubble-point pressure in pounds per square inch absolute.
OF BUBBLE-POIKT LIQUID TABLE11. PROPERTIES C = 0.66
Mole Pressure Fraction Lb./Sq.' Methane In. Abs.
Vol. Pressure Vol., Pressure, Cu. FC./ Lb./Sq.' Cu. Ft./ Lb./Sq. Lb. In. Lb. Lb. Mole In. Abs. Mole Abs. Mole Vol.
Cu. Fi./
100' F. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.65 0.7 0.75 0.8 0.85 0.9
33.4 332 671 1057 1503 2008 2520 2775 3026 3264 3467 3613 3670
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.65 0.7 0.75 0.8 0.85
245 673 1097 1518 1946 2363 2743 2915 3058 3157 3188. 3060
0.0 0.1 0.2 0.3 0.5
671 902 1112 1270 1377
WITH
2.159 2.031 1.902 1.778 1.658 1,542 1,443 1,403 1.370 1.342 1.322 1.320 1.338
280' F.
160' F. 76.8 420 802 1230 1721 2252 2758 2996 3218 3410 3550 3610 3525
220° F.
2.270 2.138 2.009 1.883 1.765 1.658 1.567 1.530 1.502 1.493 1.503 1.535 1.617 400' F.
340' F.
2.573 2.431 2.301 2.193 2.110 2,050 2.018 2.010 2.020 2.048 2.112 2.300
2,824 2.672 2.552 2,468 2.420 2.419 2.470 2.517 2,578 2.664 2.796 3.250
525 873 1203 1497 1744 1936 2071 2103 2090
... ...
... ... ...
... ... ...
3.196 3.126 3.070 3.036 3.042 3.130 3.316 3.458 3.665
... . I.
460' F. 3.836 3.948 4.085 4.282 4.602
... .,,
...
...
...
...
...
...
... ...
... ...
... ... .
.
I
80
INDUSTRIAL AND ENGINEERING CHEMISTRY 4001
300(
2'
f 200c
3Y
E loo(
MOLE FRACTION METHANE
Figure 4. Relation between Bubble-Point Pressure and Fraction When C = 0.66
ohoose, as primary variables, pressure, volume, temperature, weight, and two parameters specifying the composition of the system. The procedure in the present study consisted in determining the pressure-volume relation for a mixture having constant weight and composition a t a constant temperature. This procedure was repeated a t seven temperatures for five mixtures. Letting N1, Nd, and Nlo represent, respectively, the mole fractions of methane, n-butane, and decane in the ternary mixture, the two parameters chosen in this work t o specify the compositions of the mixtures are N1and C, where
The smoothed experimental results for all five mixtures, graphically interpolated to even values of pressure, are recorded in Table I. Within the temperature range covered by this investigation these data establish the volumetric properties of the mixtures throughout the region of pressures between bubble point and 10,000 pounds'per square inch absolute, and throughout a fairly large portion of the two-phase region adjacent to the bubble-point boundary. None of the mixtures was expanded to a sufficiently low pressure as to permit observation Qf the dew point. For mixtures rich in methane and a t temperatures high enough to avoid the two-phase region, it was possible to extrapolate graphically the compressibility factor isotherm to zero pressure, making use of the fact that the compressibility factor of any gas approaches unity as the system is expanded without limit. I n this way some reliable information was obtained concerning the volumetric behavior of the system in portions of the single-phase region at pressures less than those experimentally observed. Mole The mixture having 0.9775 p o l e fraction methane exhibited no detectable two-phase region. It is assumed that the proportion of methane in this mixture was so great as to place the cricondentherm below the lowest temperature studied. Figure 4 shows isothermal relationships between the bubblepoint pressure and the mole fraction of methane when C = 0.66. It is of interest to note that at pressures above 1000 pounds per square inch the solubility of methane passes through a minimum with respect to isobaric variations in the temperature. For example, at 2000 pounds per square inch absolute the mole fraction of methane in the bubble-point liquid has a minimum value of about 0.41 a t approximately 280' F., whereas for temperatures above and below 280" F. the concentration of methane is greater than 0.41.
The quantity C represents the mole fraction of n-butane in the n-butane-decane portion of the mixture. For the five mixtures herein reported, C had a value of approximately 0.66, and N I was varied from 0.3786 to 0.9775 (Figure 1). By holding G constant, the variation of NI may be treated graphically in a manner analogous to that employed for binary systems, the n-butane-decane mixture being regarded as one constituent and methane as the other. RESULTS
The distribution of the experimentally observed equilibrium states for a typical mixture is indicated by circled points in Figures 2 and 3. The boundary of the two-phase region, designated as the bubble-point locus in these figures, is determined by discontinuities in the slopes of the isotherms. The discontinuities are more definite in Figure 3 a t the lower temperatures, whereas a t the higher temperatures the compressibility isothernis of Figure 2 more clearly locate the boundary of the two-phase region. It may be noted in Figure 2 that a t pressures above the bubblepoint, the 100' F. isotherm cuts across the two-phase region and apparently again intersects the bubble-point locus in the neighborhood of the 220" F. bubble point. It should be realized that the isotherms shown in this figure may be regarded as contour lines on a three dimensional surface, representing intersections of that surface with a series of parallel isothermal planes. The bubble-point locus is a curve in the three-dimensional surface which does not lie in any particular plane, but intersects each of the isothermal planes a t the bubble point. The apparent dual intersection of the 100' F. isotherm with the bubble-point locus in Figure 2 is merely an illusion caused by projecting the isothermal curves upon a single pressure-compressibility factor plane.
Vol. 39, No. 1
6000
i
i9
4000
W
3
m v1 w U
a
+
z
x
2000
Y A
m m
3
m
0.2
0.4
0.6
C
MOLE FRACTION METHANE
Figure 5. Bubble-Point Pressure at 10OorF.as Related to Mole Fraction Methane for Three Values of C
5.0
W
0
;
40
t3 W
: P
30
J
5
I 20
1.0
81
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1947
0.a
04
06
08
MOLE FRACTION METHANE
Figure 6. Relation between Molal Volume at 340' F. and Mole Fraction Methane with C = 0.66
The volumetric behavior of the system a t the bubble point is recorded in Table 11. The bubble-point pressure a t 100' F. is shown in Figure 5 in relation to the mole fraction of methane for values of C equal to 0, 0.66, and 1.0. The curves corresponding to C = 0 and 1.0 were constructed from data given in earlier publications (8, 11). The curve corresponding to C = 0.66 lies, for the most part, more nearly midway between the other curves 'rather than at two thirds of the distance from the curve C = 0 to the curve C = 1.0, as would be the case if these materials behaved as ideal solutions. The isobaric-isothermal relation between the molal volume and the mole fraction of methane is shown in Figure 6 for a series of pressures a t 340" F. with C = 0.66. Although this diagram superficially resembles similar ones which may be drawn for biliary systems, there are some important differences which should be noted. In accordance with the phase rule the intensive properties of two coexisting phases of a binary system are fixed if the pressure and temperature of the system are specified. A consequence of this fact is that the isothermal-isobaric curves for molal volume plotted against molal composition in the two-phase region of a binary system are straight lines. The isothermal isobars crossing the two phase region are not straight lines in Figure 6. I n a binary system the intersections of an isothermal isobar with the boundary of the two-phase region on a volume versus composition diagram correspond to the gas and liquid phases which coexist in equilibrium with each other a t that temperature and pressure; however, this is not true in the case o f a ternary system. Points on the two-phase boundary in Figure 6 represent saturated single-phase states in which the proportions of nbutane and decane correspond to a value of C = 0.66. I n general the coexisting equilibrium phases of this system will not both contain n-butane and decane in these proportions. The greater complexity in the behavior of the ternary system over that of a binary system is a result of the additional degree of freedom introduced by a third component, which permits the intensive properties of the coexisting equilibrium phases of the ternary system to vary throughout the two-phase region eden though the pressure and temperature are fixed. Figure 7 is presented to aid in visualizing the relation of this investigation to the more extensive problem of determining the
volumetric behavior of the entire ternary system. The figure is an oblique view of a prism whose triangular base corresponds to the conventional triangular diagram for three-component mixtures. The distance along the vertical elements of the prism measured from the base corresponds to the molal volume of the system. The isothermalisobaric relation between the molal volume of the system and its composition may be represented as a surface whose intersections with the three sides of the prism describe the isothermal-isobaric , volumetric behavior of the three binary systems corresponding to those sides. These intersections are shown in the figure for the surface correponding to 340" F. and 2000 pounds per square inch absolute pressure. The dotted curve indicates the estimated locus of bubble-point and dew-point states on this surface. The nature of the -surface within the prism may be indicated either by contours generated by the intersections of constant volume (horizontal) planes with the surface in question, or by profiles generated by the intersections with the surface of vertical planes. Figure 7 shows the profile corresponding to the intersection of the plane for = o.66. in which lie all the data from the five mixtures of this investigation, with the 340" F., 2000 pounds per square inch, i s o t h e r m a l isobaric molal volume surface of the ternary
60
40
lETHANE
DECANE
02
04 MOLC FRACTIGN
I
06
20
0.8
"-BUTANE
n-BUTANE
Figure 7. Oblique View of Ternary Diagram Showing Relation between Molal Volume and Composition at 340" F. and 2000 Pounds per Square Inch Absolute
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
82
system. This profile corresponds to the 2000 pounds per square inch absolute curve of Figure 6. It is apparent that a large amount of information is necessary in order to describe in reasonable detail the volumetric properties of a ternary system throughout extended ranges of pressure and temperature. Data for a number of other profiles suitably spaced across the figure are needed. Later papers of this series will present such information. EXPERIMENTAL ACCURhCY
The sensitivity and precision of the measuring inqtruments which were mentioned earlier in this paper do not necessarily indicate the accuracy of the experimental results. Uncertainties related to the skill of the experimenter, the reliability of the calibrations, the density and distribution of the observations, and the validity of the graphical methods employed in the interpolation and correlation of the data render the exact estimation of over-all experimental accuracy very difficult. Probably the most reliable estimates of accuracy may be derived from comparisons of results from similar studies by several investigators. Wherever such comparisons are not possible, as in the present case, statements of experimental accuracy necessarily represent merely estimates based upon extended experience with the apparatus and techniques during their development and improvement, and upon those comparisons which have been possible in similar cases. The following estimates of the uncertainties in the accuracy of measurements reported here are believed to be valid :
Pressure Volume Temperature Composition
Vol. 39, No. 1 *0.1% *0.25% *0.05’ F.
*0.002 mole fraction
ACKNOWLEDGMENT
This work was carried out as a part of the activities of Research Project 37 of the dmerican Petroleum Institute. Assistance from R. H. Olds and J. A. Irwin in calculations, graphical treatment of the data, and their preparation in final form R i gratefully acknowledged. H. A. Taylor gave valuable aid in the operation of the labohtory equipment and in graphical smoothing operations. LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Beattie, Stockmayer,and Ingersoll, J . Chem. Phys., 9, 871 (1941). Bridgeman, J . Am. Chem. SOC.,49, 1174 (1927). Calingaert and Soroos, Ibid., 58, 635 (1936). Lavender, Sage, and Lacey, Oil Gas J., 39, No. 9 , 4 8 (1940). Marker and Oakwood, J . Am. Chem. Xoc., 60,2598 (1938). Olds, Reamer, Sage, and Lacey, IND. ENG.CHEM.,35, 922 (1943).
Ibid., 36, 282 (1944). Reamer, Olds, Sage, and Lacey, Ibid., 34, 1526 (1942). Sage, Budenholzer, and Lacey, Ibid., 32, 1262 (1940). Sage, Hicks, and Lacey, “Drilling and Production Practice, 1938”, p. 402, New York, Am. Petroleum Inst., 1939. (11) Sage, Hicks, and Lacey, IND.ENG.CHEM.,32, 1085 (1940). (12) Sage and Lacey, “Drilling and Production Practice, 1939”, p. 641, New York, Am. Petroleum Inst., 1940. (13) Sage and Lacey, Trans. Am. Inst. Mining Met. Engrs., 136, 136 (1940). (14) Sage, Lavender, and Lacey, IND. ENO.CHEM.,32,743 (1940). (15) Shepard, Henne, and Midgley,J.Am. Chem.Xoc., 53,1948 (1931). (16) Young, Proc. Roy. Irish Acad., B38, 65 (1928). PAPER 47 in the series “Phase Equilibria in Hydrocarbon Systems”. Previous articles have appeared during 1934-40 and 1942-46.
Recovery of Lactic Acid from Dilute Solutions ALBERT A. DIETZl WITH ED. F. DEGERING
H. H. SCHOPMEYER
Purdue University, Lafayette, Znd.
American Maize-Products Company, Roby, Znd.
I
N T H E manufacture of lactic acid by the fermentation of glucose, lactose, or other carbohydrates, the acid is obtained in
dilute solution. Difficulties due to the properties of lactic acid are encountered in its purification. Because of the relative high solubility of its salts, lactic acid cannot be precipitated quantitatively, and it cannot be rectified without decomposition because it undergoes autoesterification on heating. The difficulties involved in the manufacture of pure lactic acid are indicated by the fact that, until 1930, only commercial grades of lactic acid were manufactured in the United States (3). Smith and Claborn (9) described the preparation of a pure lactic acid by the hydrolysis of an ester. The commercial manufacture of lactic acid and the difficulties encountered in its purification were reviewed by Peckham (6) and Smith and Claborn (9). Several methods are used at present for the removal of lactic acid directly from dilute fermentation liquors. Small amounts of lactic acid volatilize with steam a t atmospheric pressure, but the distillation is not complete unless superheated steam 47) or high vacuum is used. Methodsinvolving the extraction of the acid with isopropyl ether are used, but, because of the impurities that are extracted a t the same time, i t is necessary to start with a pure 1 Present address, Toledo Hospital Institute of Medical Research, Toledo 6, Ohio.
fermentation mash (6). Extraction methods using an alcohol to extract the lactic acid (IO)have also been tried. If the alcohol is soluble in water, a solvent immiscible with water can be used to extract the lactic acid, which is then esterified in the extraction mixture. I n the present investigation a method was sought whereby it would be possible to recover the lactic acid as an alkyl lactate after its esterification in dilute solutions. Two methods were tried. First a study was made of the distill&ion of the binary and ternary mixtures of the esterification ingredients. The esters and the corresponding alcohols do not distill azeotropically. The esters and water distill azeotropically to give a distillate containing 20 to 3001, ester. This distillation has since been studied fully (2, 6), and several patents for the purification of lactic acid are based on it (8, 11, 12). I n the reported methods an alcohol is passed through a tower containing partly concentrated lactic acid, and the vapors are collected without reflux. Since no reflux is used, impurities are also carried into the distillate, and considerable hydrolysis of the ester may take place before the ester can be obtained free of aathr. I n the second method tried by the present authors, the dilute lactic acid solution (5 to 6%) is esterified and the ester extracted with a solvent in which it is preferentially soluble, The chlori-
