July, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Composition of Vapors from Boiling Binary Solutions’ D. F. Othmer EASTMAN KODAKCOMPANY, ROCHESTER, S. Y.
HE separation of the constituents of a binary solution condensed vapors p r ~ d u c e d . ~If the amount of liquid obtainand the design of distillation equipment for such recti- able in a pure state is small, the maximum sized samples disfication is dependent on the relation between the com- tilled must be small. The present investigation was therefore concerned with the position of the solution and the vapors evolved when it is distilled. Such relationships are important in the theory of development of a simple method which would minimize the solutions and their vapor pressures and also in the indus- errors mentioned above; require small amounts of liquids; trial separation of the components of such solutions. A large utilize a simple, compact, and easily operated apparatus; number of investigations have been published in this field, and give accurate results in a short time without the necesbased on four or five different methods.2 sity of complicated manipulation. The simplest method, and Apparatus that usually used in the deIn an attempt to satisfy termination of the z, y curve A simple, rapid method for t h e determination of the the foregoing requirements, (2,composition of liquid; y, relation of t h e composition of a boiling binary soluthe apparatus shown in Figcomposition of vapor, both tion a n d the vapors has been presented. The appaure 1 was devised. It is in terms of more v o l a t i l e ratus is compact, inexpensive, a n d designed to obtain blown in a single unit of component) for distillation data of such accuracy as might be required in the Pyrex glass, and may be so work, depends on the distildesign of distillation equipment. The errors of the constructed that only glass lation of part of a solution usual determination have been eliminated by the prois in contact with the mateof known composition and cedure described. Other uses of t h e apparatus, such rials to be distilled. The the condensation and analyas t h e study of the partial vapor pressures of the relative dimensions of the sis of the vapors. constituents of a binary mixture, t h e boiling-point various parts may be varied S e v e r a1 writer^^.^*^ have elevation of solutions of electrolytes, a n d the plotting within wide limits. d i s c us s e d inaccuracies inof boiling-point curves, have as yet t o be developed. The still body, A , is a herent in this method. The The x , y curves for several binary mixtures have been piece of 70-mm. glass tubmore important ones may be determined. These curves have been compared with ing 33 cm. high, and has summarized: representative ones from the literature. the bottomsealedoff slightly The possibility of a second constant boiling point 1-Ik’hen the mixture is first rounded. The vapor tube, i n t h e binary mixture of methanol andiacetone is heated, there is a fractionaB, is of 15-mm. tubing and tion of the fist vapors evolved noted. The data presented are insufficient t o estabis connected to A and the as they are condensed in heatlish this, b u t indicate it t o be a t a composition of a a u x i l i a r y j a c k e t , C, by ing the upper portion of the little over 94 per cent acetone by weight. This is still. m e a n s of a double inseal. very nearly a whole number ratio of one mol of methanol &During the progress of The vapor passes through t o ten-mols of,acetone. d i s t i l l a t i o n a part of the the elliptical hole near the vapors condense if the upper bottom of B and any small part of the still or delivery a m o u n t that condenses a t t u b e i s not protected from heat losses. This also results in partial- fractionation of the the start drains out the tip. This effectuallyprevents “primvapors. ing.” Any condensate from heat losses in C passes with the 3-When the still is initially heated, the air displaced by the vapor into the worm condenser, D, consisting of eight coils of 8vapors will be saturated and this vapor lost after passing through mm. tubing in a 38-mm. jacket. The condensate drops from the condenser. 4-The composition of the boiling solution is gradually changed the insealed tip a t the bottom of the condenser arid the rate can as the vapors richer in the more volatile component are evolved. be estimated by counting the drops. The capacity of E deterThis change also affects the composition of the vapors. The subsequent analysis of the condensate from the vapor gives the mines the size of condensate sample obtainable for analysis. average composition of the vapor, but analysis of the sample of Condensate fills E until the inverted trap runs over and the the liquid taken either before or after distillation will give a condensate is returned to the boiling liquid. The vent tube, value respectively too high or too low in the more volatile com- G, covered loosely with a glass cap during operation, allows ponent. both E and F to be maintained a t the atmospheric pressure. The last-mentioned error may be minimized by using a If readings a t other pressures are desired, this tube would be large amount of liquid in the still. I n any event, the ratio connected to a manometer and suitable pressure-regulating of the volume of initial liquid to the volume of the condensate system. The branch tubes and cocks J and K serve for the from the vapor must be very large. If the condensed solu- withdrawal of samples of condensate and boiling liquid, tion is to be analyzed by chemical methods, the analysis is respectively. The thistle tube, L, and cock serve for the inusually more simple and accurate if samples as large as 10 cc. itial charging and subsequent additions of liquid, as well as may be utilized. The amount of liquid in the still should for a relief valve for the air originally present in the still usually be from one t o two hundred times the amount of body. If it is desirable to use the apparatus for boilingpoint and partial-pressure determinations as well as for vapor1 Received March 29, 1928. Presented before the Division of Incomposition curves, a thermometer supported in the tube B dustrial and Engineering Chemistry at the 75th Meeting of the American is necessary. The simplest support is by means of a rubber Chemical Society, St. Louis, Mo..April 16 to 19, 1928. * Young, “Distillation Principles and Processes,” p. 62, Macmillan or cork stopper as is shown. An alternate method for use with
T
Co., 1922. 8 Rosanoff, Lamb, and Breithut, J . A m . Chem. Soc., Si, 448 (1909). 4 Rosanoff and Easley, I b i d . , Si, 953 (1909).
Zawidzki, 2. physik. Chem., S5, 129 (1901). This apparatus was satisfactorily constructed by the Technical Glass Company of Rochester, N. Y. 6
e
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
materials affected by contact with rubber or cork is shown in the inserted sketch. A Pyrex stopper with a small ring formed in the under side is ground to fit, and supported from this ring is a fine platinum wire leading to a short-scale thermometer of the Anschuta type. The thermometer is entirely surrounded by the vapors and is read through two thicknesses of glass. Heat is supplied to the boiling liquid by the Gilmer heater, N . A sheet-iron cone, formed as shown and covered with asbestos paper, was cemented to the opening in the top of the heater. Rate of boiling may be controlled by an external rheostat or by elevating the apparatus above the cone. A Bunsen flame was also found satisfactory when non-inflammable liquids were being studied. The apparatus has been designed t o maintain a constant c o m p o s i t i o n of the liquid in the boiling chamber during the d i s t i l l a t i o n of the vapor samples. This \ is a c c o m p l i s h e d by returning to the boiling liquid the same amount of each cons t i t u e n t as is being evolved in the vapor 1 by means of the overflow, F.
w
Operation
The determination of the vapor-composition c u r v e s t a r t e d with the charging of the still body with a binary solution, usually with only a small p e r c e n t a g e of the high-boiling constituent. Heat was supplied, the s o l u t i o n b o i l e d , and the air Figure 1-Apparatus for D e t e r m i n a t i o n originally present exof C o m p o s i t i o n of Vapors from Boiling pelled through L and Binary S o l u t i o n s H . W h e n vaDors issued through L, the cock was closed and the tube B was jacketed with the same vapor it was carrying and heat losses to the vapor going to the condenser almost entirely eliminated. Note-Only
a very small amount of condensate was formed in the tube Depending on the boiling point and latent heat of the liquids employed, this was a drop every 3 to 15 minutes. The amount of fractionation due to such a low reflux ratio in this straight tube must he very small. It may be reduced even more by covering the outer tube with insulating material. Standard magnesia pipe covering is easily applied or any loose packing could be supported in a suitable container. An additional precaution against cooling of the vapor due to partial condensation in the top of the boiling chamber would be to withdraw continually a small amount to a reflux condenser, the condensate being returned to the boiling liquid. The degree of accuracy desired in the use of this apparatus will determine the necessity of such refinements.
B , owing to heat losses.
The vapor and a very small amount of liquid which condensed in C passed into the condenser. The first distillate was run to waste through the cock J; then the reservoir E and the adjacent limb of F were filled. During this process the boiling temperature gradually increased, owing to the depletion of the more volatile component in the boiling liquid. The level in E finally reached the overflow level of F and then remained constant, the condensate flowing back into the still
Vol. 20, No. 7
body, A , as fast as it was formed. As liquid from E flowed into the still pot, the temperature usually decreased slightly owing to the addition of a liquid richer in the more volatile component. A steady state was indicated in most cases when the thermometer was stationary, but in those binary mixtures having a portion of the vapor-composition curve very close to or crossing the 45-degree line, a change in the composition of the vapors coming off, which could be detected in the subsequent analysis, would be indicated by a change in temperature too small to be recorded by the thermometer. The usual procedure, therefore, after the thermometer indicated a constant temperature, was to allow as much liquid to be distilled, condensed, and run back into the still body as would fill E several times. A steady state was thus insured before samples were taken. A two-hole rubber stopper for a test tube was fitted on the draw-off, K . To insure a representative sample of the boiling liquid a small amount was run out to waste. A test tube, previously cooled in a freezing mixture, was brought up around the stopper, and the required amount of the solution was drawn into it, the air displaced rising through the open hole of the stopper. The same procedure was immediately followed in drawing the condensate sample, but since this liquid came from the condenser relatively cold, there was not so much danger of volatilization. The composition of the boiling liquid was changed before, proceeding with the second determination. This could be accomplished either by draining the material present and filling with a fresh solution of a predetermined composition, or by the addition of a small amount of the less volatile component. The latter method was adopted and the amount needed was determined by the change in the boiling point and by rough calculations of the initial composition and the probable amounts of the two constituents drawn off in the samples. I n this manner condensate and liquid samples were obtained over the whole range desired. An alternate method of operation (which has never been used) would be to start with a weighed solution of accurately determined composition and take only the condensate sample after a steady state was attained, This sample would have, in the ordinary case, a higher concentration of the more volatile liquid, and if the amount and concentration were determined the composition of the solution remaining in the system could be determined. Successive samples would deplete the mixture of the more volatile compound and the analyses of condensate and corresponding calculations would serve to plot the whole curve. This involves cumulative analytical errors and in most cases the method used would be more simple and accurate, although it necessitates more analytical work. Materials
The vapor-composition curves of four binary solutions are shown in the figures. These are not the only curves which have been determined with this apparatus nor have they been chosen except to illustrate the application of the method to the three types of binary solutions: (1) those which boil a t temperatures between the boiling points of the pure components, (2) those with maximum boiling points, and (3) those with minimum boiling points. The first two solutions, acetic acid with water and acetic acid with benzene, have normal boiling-point curves; the third solution, hydrochloric acid with water, has a maximum boiling point; and the fourth solution, acetone with methanol has a minimum boiling point. The acetic acid used in the first two binary mixtures was a good grade of glacial acid, the only impurity shown by analysis being a small amount of water, which was immaterial in the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July, 1928
Water in liquid Figure 2-Water and Acetic Acid
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Hydrochloric acid in liquid Figure 4-Hydrochloric Acid and Water
Benzene in liquid Figure 3-Benzene and Acetic Acid
Figures 2 to 5-Vapor-Composition Curves
f i r s t determination. To remove this fraction of a per cent for t h e second series, about 10 per cent of the benzene to be used w a s a d d e d and the mixture distilled. The distillate above 116" C. was used for the d e t e r m i n a t i on. This procedure makes Acetone in liquid an anhydrous acid by Figure &Acetone and Methanol removing the water in a n azeotropic mixture with benzene, but leaves 1or 2 per cent of benzene in the acid. For the present use there was no necessity of removing this by further fractionation. The benzene was "Eastman" quality from the Department of Synthetic Chemistry of the Eastman Kodak Company. It was free from thiophene and froze a t 5.4" C. The hydrochloric acid was Baker's Analyzed. The acetone used was a specially purified product redistilled over powdered calcium chloride and fractionated in a ten-trap Clarke9 column. Ninety-five per cent of a large sample came over within a tenth of a degree and that part used was in the middle of this fraction and distilled without apparent change of temperature. The methanol used was of "Eastman" quality, acetone-free and boiling between 64.5"and 65" C. Analysis
The composition of the samples was determined chemically, the first three pairs by titration of the acid content, the fourth by the Messingers method for the determination of acetone. Data Obtained
The numerical results are presented in the tables and in the figures. The boiling temperatures which are recorded in Tables I1 to IV were taken with a thermometer graduated to 0.5" C. and calibrated by the Bureau of Standards. I n that part of the scale used, the certificate showed the error to be within the errors of reading. While these temperatures were not used, they are submitted in order that boiling-point curves may be drawn and partial pressures calculated from these data, if desired. 7 IND. ENG. CHEM., 18, 1092 (1926). Griffin, "Technical Methods of Analysis," p. 95, McGraw-Hill Book Co., 1927.
Table I-Water a n d Acetic Acid WATER WATER IN LIQUID I N VAPOR Wt. %
Table 11-Benzene a n d Acetic Acid (Barometer, 758 mm.) BENZENE BENZENE TEMP. IN LIQUID IN VAPOR O c. % W f .%
Table 111-Hydrochloric Acid a n d Water (Barometer, 7 5 1 . 3 mm.) HCI HC1 TEMP. IN LIQUIDIN VAPOR
c.
107.3 107.5 107.6 107.8 107.2 105.5 103.1 101.5
wt.%
Wt. %
21.79 21.36 20.79 20.09 18.09 15.97 12.45 8.67
31.00 27.54 22.97 18.49 7.55 2.80 0.75 0.21
wt.
Table IV-Acetone and Methanol (Barometer, 755 mm.) ACETONE ACETONE TEMP. IN LIQUID I N VAPOR oc. W f .% Wt.% 55.2 95.8 96.0 55.0 92.9 92.1 54.7 89.9 88.7 54.9 81.4 83.3 67.0 73.5 55.4 56.6 58.8 88.3 56.8 45.2 62.0 31.8 51.8 58.3 61.9 9.6 23.4
The x and y curves, Figures 2 and 5, are plotted with weight per cents of the more volatile component in the liquid as abscissa and weight per cents of the more volatile component in the vapor as ordinates. The experimental points of the present determinations are connected by the solid lines. I n Figure 2, the dotted line is from Lord Rayleigh.' The results of two other investigators are reported by Hausbrand.10 The data of Bergstrom are considered by Hausbrand as being the most reliable, and agree with the results of the present work so nearly that the curve coincides with that drawn. Four determinations by Blacher reported by Hausbrand fall between the two curves of Figure 2. The dotted line in Figure 3 is from Rosanoff and Easley.' The curve for hydrochloric acid and water cannot be obtained for acid of much higher concentration than 25 per cent without artificial refrigeration in the condenser. The data for weaker acid are represented by Figure 4. The dotted curve is from Lord Rayleigh.4 The maximum boiling pointi. e., the point where the vapors have the same composition as the liquid-was found to be the same in the present determination as that given by Lord Rayleigh, but his other data, in the curve for acetic acid and water, show the vapor composition more nearly the same as the liquid composition than that shown in the present determinations. The data of Pettitl' for methanol and acetone are indicated by the dotted line and that of Bergstrom,loby the light line in Figure 5. This curve is of industrial interest because 0 10
Pkrl. Mag.,161 4, 521 (1902). "Principles and Practice of Industrial Distillation," p. 131, John Wiley
& Sons, Inc., 1926. 1'
J . Pkrs. Chem., 8, 340 (1899).
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the separation of mixtures containing less than 12 per cent of methanol has long been known to be impossible by simple rectification methods. The constant-boiling mixture is usually given as 86.5 per cent of acetone, and a t this point the plotted curve crosses the 45-degree line. The three determinations with an acetone content above this constantboiling mixture seem to indicate that the line is crossed a second time a t about 94 per cent. A constant boiling point indicated by the line crossing in this manner would be maximum. The curve of Pettit does not cross the line to indicate the con-
Vol. 20, No. 7
stant boiling point, butit does showa greater differencebetween the vapor and liquid composition a t 97 per cent acetone than at 94 per cent. This irregularity in the curve of Pettit could be explained if it crossed the line a t the constant boiling point as it should. Then, as in the case of the present determination, it would be indicative of a second constant-boiling mixture. The presence of this second constant-boiling mixture is more probable than the type of vapor composition curve shown by Pettit or the coincidence of the curve with the 45-degree line as is more usually supposed.
Dissolved and Suspended Mineral Matter in Colorado River'*' W. D. Collins and C. S. Howard UNITED STATES GEOLOGICAL SURVEY, WASHINGTON, D.
OLORADO River has a drainage area of 242,000 s q u a r e miles, nearly half as large as the d r a i n a g e area of Missouri River a t St. Louis and 40 per cent more than the drainage area of Mississippi R i v e r above St. Louis. The average discharge of C o l o r a d o River is, however, less than one-fourth the average discharge of Missouri River, or one-f if t h the average discharge of the upper Mississippi a t St. Louis. The average discharge is much less than that of S a c r a m e n t o River, which drains a b o u t one-eighth the area drained by the Colorado, and is not very different from the discharge of Alabama River or Hudson River, either of which has hardly one-sixteenth the drainage area of the Colorado.
C
c.
Studies of Colorado River by the United States Geological Survey during the last three years confirm earlier reports as to the dissolved and suspended matter in the river. The dissolved solids range from about 250 to about 1500 p . p . m . Therefore, the water can be used for irrigation if suitable drainage is provided. At its best the river would make a fair source of water for domestic use. At its worst the concentration of dissolved solids is far beyond any limit generally recognized as permissible for a public supply. A reservoir holding the discharge of the river for a year would furnish an average water that could be used for a public supply, though its content of over 500 p. p. m . of dissolved solids would put it in the class of the poorer public water supplies. The suspended matter will cause a loss of capacity of any reservoirs on the river. The 225,000,000 tons of suspended matter carried in 1925-26 and the 443,000,000 tons carried in 1926-27 are considerably greater than the quantities generally reported. No accurate estimate can be made of the space in a reservoir that would be occupied by this material until careful studies are made to determine the weight of solid material in a given volume of deposit.
Table I-Drainage Areas a n d Average Discharges of S o m e Rivers of the U n i t e d States, S t a t e d in Percentages Referred to Colorado River [Data compiled by G. C.Stevens, U. S. Geological Survey] DRAINAGEAVERAGE RIVER AREA DISCHARGE Per cent Per cenf Colorado 100 100 Missouri 217 426 Upper Mississippi (above the Missouri) 70 540 Sacramento 13 140 Alabama 6.3 118 Hudson 5.5 89
Part of the interest in Colorado River and some of the disagreements regarding its utilization result from the unequal contributions to its volume from the different states through or past which it flows. It has been estimated by G. C. Stevensa that 64 per cent of the water comes from 15.5 per cent of the drainage area (Colorado), and 89 per cent from 38.6 1 Received March 17, 1928. Presented before the Division of Water, Sewage, and Sanitation at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. Published by permission of the Director, United States Geological Survey. 8 Personal communication,
per cent of the area (Wyoming, Colorado, Utah). Arizona, with 45 per cent of the drainage area drained by the river, contributes 4 per cent of the flow; California, with 1.6 per cent of the area, contributes almost nothing. In connection with studies of the discharge of Colorado River it has been possible to obtain samples of water for analysis and samples of the silt carried by the river. The greater part of the samples have been taken by observers r e g u l a r l y stationed a t the river a t Bright Angel Creek near Grand Canyon and near Topock, Ariz. Daily samples of water have been collected a t these two points since a b o u t September 1, 1925, and a t Yuma, Ariz., since October 1, 1926. Occasional single samples or short series of samples have been taken at other points on the main river and tributaries. During the first year seven daily samples were combined to make a composite. Since that time the daily samples have been combined to give three composite samples each month. The analyses made for the year 1925-26 have been p u b l i ~ h e dand ,~ the analyses for 1926-27 have been prepared for publication. Typical analyses and certain averages are given in Table 11. Analyses 5 and 9 are averages of the single analyses of the composite samples for the period covered. Analyses 6 and 10 are weighted averages intended to show the composition of water in a reservoir that would contain the total flow for one year. They show it only approximately, however, because the composite samples contained nearly equal quantities of the daily samples and not quantities proportional to the daily discharges. The weighted averages were calculated by multiplying the figures in the analyses of the composite samples by the average discharge for the period covered by each sample, and dividing the sum of the products by the sum of the discharges. The other averages accurately represent the composition of the water that would be collected 4
Collins, U. S. Geol. Survey, W a f n - S u p p l y PaQer 696, 33 (1927).
