Nitromethane-Isopropyl AlcoholWater Svstem J
Vapor-Liquid Equilibria in the Ternary System and in the Three Related Binary Systems J. E. SCHUMACHER ANI) HERSCHEL HUNT Purdue University, Lafayette, Ind.
The mutual solubility of nitromethane and water has been determined. The ternary phase diagram of nitromethane-isopropyl alcohol-water has been determined. The vapor-liquid equilibria data for the binary and ternary systems are also given. The ternary and binary mixtures form minimum-boiling azeotropes. A means to recover nitromethane from the three-component mixtures is suggested.
methane to the extent of 2.28 per cent by weight a t 25' C. and that nitromethane was soluble in water to the extent of 11.03 per cent by weight. The solubility diagram for the ternary system was determined in a manner similar to Fowler's method for the ternary system nitromethane-n-propanolwater (6). Throughout this discussion all percentages are by weight.
Equilibrium Data The vapor-liquid equilibria data are graphed in Figure 1. Each binary system exhibits a constant-boiling mixture (C. B. M.). The straight horizontal section from 14.5 to 73.0 per cent water on the nitromethane-water equilibrium curve (Figure 2) represents a two-phase region at the boiling point. Considering these end points at their temperature (83.6' C.),
HE system nitromethane-isopropyl alcohol-water was investigated, and the vapor-liquid equilibrium diagrams were determined for the ternary system and the three related binary systems. The equilibrium apparatus was essentially the same as that used by Fowler (6) and Baker (1). It was standardized by repeating the work of Carey and Lewis (3)on the ethyl alcohol-water system. The analysis for percentage composition of the mixtures as well as distillation procedures were performed in the same manner as described by Fowler. The nitromethane was Commercial Solvent's technical grade, fractionated to obtain a cut boiling a t 101.0-101.7" C. a t 760 mm. Its purity was checked (10) by determining the density a t 25 'C. to be 1.129 grams per cc. The isopropyl alcohol was Carbide and Carbon's technical grade, thoroughly dried over Drierite and fractionated to a cut boiling a t 82.0-82.3' C. a t 760 mm. Its density at 25' C. was 0.7803 gram per cc. Distilled water was used in all the experimental work. , Refractive index measurements on various mixtures of nitromethane and water showed FIQUR 1.~ VAPOR-LIQUID EQUILIBRIAI N THE TERNARY SYSTEM NITROMETHANXIthat water was soluble in nitro2-PROPANOL-WATER 701
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Vol. 34, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I.
COMPOSITION AND B o I L I N a P O I N T S OB
Binary System Isopro yl alcohol-nitrornet%ane Isopropyl alcohol-water Nitromethane-water
AZEOTROPES
BINARY
Azeotropic Data Experimental __ Literature B. P.,' B. P Compn., % 0 C. Compn., % 0 c."
23.6 water
83.6
21.8 water
83.7 (6)
nearly constant as possible, the percentage of isopropyl alcohol was held constant. I n the case of the 60 per cent constant composition of isopropyl alcohol two batches were made up-one of 60 per cent isopropyl alcohol and water, the other 60 per cent isopropyl alcohol and nitromethane. Varying proportions of these batches were introduced into the still to give several consecutive runs with a constant percentage of alcohol in the liquid. The ternary samples were analyzed by the method suggested by Baker (1). Curves were plotted by measuring the WT % A IN LIQUID refractive indices and densities of mixtures composed of nitromethane and isopropyl alcohol, each with a definite conFIGURE 2. VAPOR-LIQUID EQUILIBRIA IN THE BINARYSYSTEMS stant percentage of water. The composition of alcohol and nitromethane was varied until the critical solubility point was reached; this point in each case was determined from the teran approximate plot of temperature us. solubility for the ninary solubility diagram. The intersections of' the refractive index or density ordinate with the constant weight per cent of tromethane-water system can be made. In addition, the critical solubility of 35 per cent water a t 103' C. (9) and the water lines gave points which were plotted on the ternary mutual solubility of the components a t 25' C. must be conanalysis diagram of Figure 3. From this chart the experisidered. mental data were interpreted as per cent composition. Table I lists the boiling points together with the compositions of the binary C. B. M.'s. The data found in the literature are also included. Lebo (6) gave data for water-2propanol. The check in boiling points indicates no radical error in technique. The discrepancies in the compositions of the C. 13. Me's are somewhat more pronounced. It is believed that the v a p o r - l i q u i d e q u i l i b r i u m method is capable of greater accuracy in determining the compositions of these C. B. M.'s than the boiling p o i n t - composition d i a gram used by Lecat. The only major difference in determining the ternary equilibrium diagram and the binary equilibrium diagrams was that, in order to correlate data, it was necessary to make several runs having app r o x i m a t el y t h e same percentage of one component in t h e liquid. Wi?% /N 7H' LIQUID I n order t h a t these amounts should be as F I G U R E 3. ANALYSISO F T H E TERNARY SYSTEM
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INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1942
TABLE11. DATAFOR
THE TERNARY SYSTEM ISOPROPYL ALCOHOLNITROMDTHA~-WATIR
.
,
Equilibrium Data --Liquid Data, 9’ -Va or Data, %Isoprop 1 d i Z Isopropy? Nitroalaoho? Water methane alcohol Water methane 8.0 18.2 80.0 10.0 10.0 73.8 9.5 12.2 80.0 78.3 14.0 0.0 5.8 20.6 80.0 73.6 6.0 14.0 10.9 26.5 21.4 60.8 62.6 17.8 13.2 18.0 59.2 68.8 8.8 32.0 7.6 29.4 60.7 63.0 26.0 13.3 34.5 58.8 59.5 36.8 4.4 6.0 13.2 25.7 50.0 61.1 14.2 35.8 39.5 49.8 53.0 38.4 11.8 7.5 35.1 49.9 53.4 19.8 11.5 30.3 12.6 31.3 49.5 56.1 20.5 30.0 31.6 39.4 12.8 55.6 16.6 44.0 20.9 38.4 65.8 53.6 13.3 8.0 42.0 11.0 39.6 47.0 17.0 43.4 40.7 39.6 46.0 25.4 13.3 35.0 39.4 39.1 47.0 13.6 24.6 36.3 13.1 43.4 24.6 43.5 54.2 21.3 32.1 23.7 53.9 64.8 14.0 11.5 49.1 25.0 39.1 11.8 70.0 5.0 47.2 37.7 15.1 28.0 43.0 29.0
-Solubility
Data,?
Isopropyf alcohol 0.0 13.6 21.6 23.9 24.1 24.2 24.2 24.3 24.3 23.1 21.4 17.2 13.2 0.0
NitroWater methane 89.0 11.0 12.9 73.5 19.5 58.9 26.6 49.5 26.8 49.1 41.5 34.3 34.2 41.6 34.1 41.6 41.7 34.0 50.1 26.8 19.6 59.0 70.4 12.4 77.8 9.0 97.7 2.3
7 ’ ’ a t 2bo C.
The vapor-liquid equilibrium data for the ternary system are presented in Table 11,and for the binary systems in Table 111. Several sets of data for the ternary system have nearly the same percentage of isopropyl alcohol in the liquid. The nitromethane vapor-liquid equilibria a t constant per cent isopropyl alcohol is graphed for each of these different sets of data. The water equilibria diagrams were similarly plotted. The variations evident in the different sets of data in Table I1 do not detract from the utility of the data since it was assumed that the relative volatility of the components remained constant over the small range of composition in each set. Moreover, examination of the equilibrium curves shows that those representing widely varying “constant” percentages of isopropyl alcohol in the liquid lie close together. On these bases it was considered proper to draw the equilibrium curves a t the constant per cent alcohol intended in each case. I n order to present the data in a more convenient and usable form, the data from curves of weight per cent water in the vapor us. weight per cent water in the liquid, and weight per cent nitromethane in the vapor os. weight per cent nitro-
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methane in the liquid were transcribed to the triangular graph of Figure 1. Here the curves represent constant percentages of water and nitromethane in the vapor. They were determined from the individual graphs mentioned above by followinga constant vapor weight per cent ordinate through the varying compositionsin the liquid and locating the intersection with each constant weight per cent isopropyl alcohol curve. Careful study of Figure 1 indicates a constantboiling mixture of 6 per cent water, 32 per cent nitromethane, and 62 per cent isopropyl alcohol. The boiling point of this C. B. M. was determined as 78” C.
Industrial Application The following procedure is offered as a method to Durifv nitromethane contaminated with isopropyl &oh01 and water if such a mixture should occur in any industrial process concerned with these components. It is obviousfrom the ternary diagram that the azeotropic mixture which is obtained as condensate on batch distillation of any mixture of the three components cannot be resolved into its relatively pure components merely by adding one pure component with the object of causing a separation into two phases. Figure 3 may be divided into three regions with a common point a t the ternary azeotropic composition. If we start with a mixture having a composition in any one of these regions, the pure component of this region ultimately will be left as residue after fractional distillation. It may not be practical to add water and nitromethane to the azeotrope in order to obtain two phases so that the phase rich in nitromethane might be used to prepare pure nitromethane. However, the ternary azeotropic mixture may be separated into its components by adding ammonium nitrate to the azeotrope at its boiling point. This gives a two-phase mixture, one of which is an aqueous solution saturate with ammonium nitrate, while the other is primarily isopropyl alcohol and nitromethane. Any appreciable amount of water remaining in the isopropyl alcohol-nitromethane layer may be removed as the ternary azeotrope by batch distillation. The
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TABLE111. EQUILIBRIUM DATAOF BINARY SYSTEMS Nitromethane-Isopropyl Isopropyl Alcohol-Water Nitromethane-Water Alcohol % 2-propanol Refraative % water Yo water Refractive % a!cohol % alaohol by wt. index (20” C . ) in liquid in vapor4 % water index (ZOO C.) in liquid In vapor 89.7 5.00 1.337 91.3 2.5 13.0 1,3813 0.72 2.90 17.3 10.00 1.342 89.0 90.0 5.4 19.7 1.3811 0.99 6.40 32.0 87.9 15.00 1.346 88.4 8.2 22.0 1.3805 1.78 42.7 11.9 1.351 87.0 20.00 86.8 11.5 22.8 1.3802 2.03 17.5 48.5 85.9 25.00 1.364 84.7 16.0 23.6 1.3800 3.04b 49.3 17.8 1.358 84.9 30.00 82.6 19.9 23.6 3.97s 24.2 1.3800 53.6 83.9 35.00 1.361 80.0 27.9 23.6 1.3800 5.00b 24.7 54.3 83.3 1.364 78.0 40.00 34.6 23.6 87.16b 1.3400 31.9 57.4 82.6 1.366 45.00 44.2 23.5 75.8 1.3400 41.5 87.87b 60.1 82.2 1.368 73.5 60.00 49.7 23.5 42.1 88.85b 1.3400 61.8 1.370 65.00 81.8 72.7 66.6 23.3 1.3395 47.6 89.93 63.7 1.371 80.9 68.0 60.00 68.5 23.5 1.3390 47.9 90.93 63.0 1.373 65.00 80.5 65.0 75.3 23.7 1.3385 53.4 91.98 65.5 1.3745 80.1 62.8 70.00 78.0 24.0 1,3380 92.98 58.1 66.4 79.9 1.3765 61.6 80.00 81.2 25.2 1.3371 58.6 94.07 66.9 80.0 1.3776 90.00 59.3 85.0 27.2 52.5 67.9 79.7 1.3776 100.00 58.1 87.3 28.8 66.6 69.3 79.2 52.0 91.7 36.1 66.8 69.4 78.8 44.0 92.6 39.2 70.5 71.2 78.3 41.8 95.4 52.5 74.3 73.1 77.7 33.0 77.5 75.2 77.0 24.0 78.5 75.5 75.2 17.3 81.7 77.5 74.8 17.5 85.1 79.9 71.8 11.6 88.1 82.4 70.8 10.7 91 .O 85.0 63.3 7.20 52.6 5.00 0 These data show the vapor to be slightly richer in water than do the data of Fowler and Hunt. The authors were aware of this a t the time of the experimentation, and since the present data were obtained repeatedly they must take preaedenae over the former data. b Two phases: the data are for the water phase. Fna&o$l
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INDUSTRIAL AND ENGINEERING CHEMISTRY
isopropyl alcohol and the nitromethane appear in the ternary azeotrope as 62 and 32 per cent, respectively, together with 6 per cent water. However, in the binary mixture, after the separation of the saturated ammonium nitrate solution, these components are present as approximately 66 per cent isopropyl alcohol and 34 per cent nitromethene. Since this amount of alcohol is less than the percentage present in the minimum-boiling isopropyl alcohol-nitromethane C. B. M., it is possible t o obtain pure nitromethane by batch distillation of the recovered binary mixture. The condensate from this distillation process will have the composition of the nitromethane-isopropyl alcohol azeotrope.
Vol. 34, No. 6
Bibliography (1) Baker, E. M., Chaddock, R. E., Lindaay, B. A., and Werner, R. C., IXD.ENG.CHEM.,31, 1263 (1939). (2) Baker, E. M.,Hubbard, R. O., Huguet, J. H., and Mickalowski, L. L.,Ibid., 31, 1280 (1939). (3) Carey, J. L., and Lewis, W. K., Ibid., 24, 882 (1932). (4) Carveth, H . R., J . Phys. Chem., 3, 193 (1899). (5) Fowler, A. R., and H u n t , H . , IND. ENQ.CHEM.,33,90 (1941). (6) Lebo, R.B., J . Am. Chem. SOC.,43, 1005 (1921). (7) Leoat, M., 2. anorg. Chem., 186, 119 (1930). . ANAL.ED., 4, 232 (1932). (8) Othmer, D. F., IND. E N @ CHEW, (9) Timmermans, Z . , Phys. Chem., 58, 29 (1907). (10) Washburn, E. W., in International Critical Tables, Vol. 111, pp. 33, 35, 219, 318 (1928).
Loss of Plasticizers from
Polvvinvl Chloride Plastics J
J
in Vacuum H. A. LIEBHAFSKY, A. L. MARSHALL, AND FRANK H. VERHOEIC‘ General Electric Company, Schenectady, N. Y.
PON being molded, polyvinyl chloride, an amorphous white powder, yields a hard, brittle, and therefore relatively useless, material. But if a “plasticizer” (usually a liquid) is properly added, a soft, flexible plastic is formed. How polyvinyl chloride and plasticizer interact to produce this change is not well known; the extent, conceivably even the type, of interaction may vary from case to case. A study of the way in which plasticizers leave a plastic can shed sonie light on the problem. Because the situation is complex, simple experimental conditions are highly desirable. Heating the plastics in sufficiently high vacuum ensures that no plasticizer molecule, having once evaporated, will ever return to the plastic surface; and that diffusion of the plasticizer through the plastic will eventually determine the rate a t which plasticizer is lost, which makes it possible t o obtain the corresponding diffusion constants from measurements of the rate of loss. Such measurements are reported for the plasticizers tricresyl phosphate, dibutyl phthalate, and dibenzyl sebacate. The results have been treated on the assumption that the surface concentration of plasticizer drops instantly to zero a t the beginning of each experiment and remains zero thereafter. This treatment is applicable until some 30 per cent of the plasticizer has been lost, whereupon complicating factors enter whose effect becomes more pronounced as the loss of plasticizer proceeds.
U
Preparation of Plastics Plastics are usually prepared by milling, which “strains”
the material so that marked dimension changes may occur on 1 Present
address, Ohio State University, Columbus, Ohio.
subsequent heating. Our plastics were prepared by the method of R. M. Fuoss of this laboratory, in which there is no milling and the composition of the produc1,s is accurately known. Weighed quantities of polyvinyl chloride and of plasticizer were thoroughly mixed by grinding for 15 minutes in a glass mortar after they had been stirred together for 5 minutes in a small beaker. The wet, muddy mixture that resulted was transferred to a tall-form beaker and heated for 6 minutes in a liquid bath near 90” C. During this heating, the material changes gradually to a dry, rubbery powder, and the risk of subsequent stray losses is thus decreased. After a second thorough grinding in the mortar, the mixture was transferred to a steam-jacketed positive mold, 4 inches in diameter, to which was attached a vacuum line for the removal of entrapped air. Heat and pressure were applied according to the following schedule: Compression was begun when the temperature of the mold had reached 110’ @.; the full pressure, 2500 pounds per square inch (176 kg. per sq. cm.), was reached 10 minutes later, a t which time the temperature had risen to 145’ C. Pressure and temperature were then maintained for 5 minutes, whereupon the mold was cooled and removed from the press. The molded disk and all scraps were carefully collected and weighed. The disk was finally aged for 1to 1.5 hours in an oven a t 104” C. Except for a slight peripheral shrinkage in the region that had been nearest the vacuum line attached to the mold, our plastics did not change dimensions during aging. The composition of one sample was verified by a chloride determination: found, 40.46 per cent polyvinyl chloride; calculated (with corrections), 40.39 per cent. These losses were allowed for in calculating the composition of an 11-gram sample: 20-30 mg. (presumably of the initial composition) left in the mortar; 10-100 mg. (plasticizer only) lost during molding; 20-30 mg. (plasticizer only) lost during aging.
