FEBRUa4RY, 1938
where V
= size of solvent a, b = constants
INDUSTRIAL ARTDENGINEERING CHEMISTRY
molecules
199
The compositions giving the minimum viscosity as revealed by this work rarely coincide with the compositions giving the maximum dilution ratio as determined in the first section of the paper. 3. The viscosities of solutions involving esters can be considerably reduced by coupling the esters with alcohols, but very little reduction in viscosity can be effected by coupling ketones with alcohols. 4. Secondary alcohols are more effective in reducing the viscosities of solutions made with n-butyl and n-amyl acetates than are the corresponding primary alcohols, although the differences are very slight. On the other hand, ethyl alcohol, a normal compound, is more effective in reducing the viscosity of solutions made with isopropyl acetate, a secondary compound, than is the corresponding secondary alcohol, isopropanol. 5 . The relative viscosities'of solutions of nitrocellulose in the pure members of homologous series fall on straight lines when plotted against the molar volumes of the solvents.
Figure 12 shows that the relative viscosity increases ( a is plus) as the size of the solvent molecules increases in the case of both normal esters and normal 2-ketones, but decreases (a is minus) in the case of the normal ether-alcohols. The reversal of the slope in the case of the ether-alcohols is due t? the fact that the viscosity of the solvent increases faster than the viscosity of the solution as we ascend the homologous series.
Summary 1. The viscosities of 8 per cent solids solutions of nitrocellulose in the pure solvents belonging to homologous series of normal acetic esters, normal 2-ketones, and normal etheralcohols increase continuously as the size of the solvent molecules increases. 2. Data showing the relation of the viscosities of 8 per cent solids solutions of nitrocellulose in mixtures of solvent and coupler to the composition of the mixtures are given for twenty-six different combinations of solvent and coupler.
RECEIVEDDecember 13, 1937.
Phase Diagram Method of Solvent Evaluation
I
cosity method and the dilution ratio method are combined on a single chart or phase diagram. This method of evaluation defines precisely the regions (compositions) in which it is more desirable to formulate and the regions that must be avoided, and has the advantage of expressing quantitatively the physical state of complete systems involving the resinous material, solvent (plus coupler), and diluent. The phase diagram method was developed in connection with a study of solvents for Vinylite3 resins, which cannot be evaluated satisfactorily by dilution ratio comparisons. The general usefulness of the method was a t once apparent, however, and the study was extended to include solvents for other resinous materials besides Vinylite resins. I n this section, therefore, the application of the phase diagram method of solvent evaluation to solvents for nitrocellulose will be given. The dilution ratio is defined as the ratio by volume of diluent to solvent when a mixture of two such liquids just fails to dissolve nitrocellulose. The determination is usually carried out by titrating a solution of nitrocellulose in the solvent with
N T H E preceding sections, solvents and solvent-coupler
mixtures were compared by means of their toluene dilution ratios and by the viscosities of their nitrocellulose solutions. Neither of these methods is adequate to evaluate the strictly solvent characteristics of these liquids, as distinguished from their use characteristics such as evaporation rate, stability, blush resistance, color, and odor. A system for the complete evaluation of the solvent characteristics of solvents for resinous material has been worked out in this laboratory whereby data determined by both the vis-
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FIGURE 13. EQUILIBRIUM VISCOSITY DIAGRAM O F hTITROCELLULOSE IN 85 PER CENT ETHYL MIXTURESAT 20" C . ACETATE-TOLUENE
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INDUSTRIAL 4ND ENGINEERING CHEMISTRY I40
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The study of the viscosity relations is more complicated. To obtain the viscosity data, several series of solutions are made up in such a manner that the solutions of each series are of approximately the same solids content. The thinner composition of the solutions of each series is varied from pure solvent to a high proportion of nonsolvent. The solutions are aged a t 20' C . in a thermostatic bath for several weeks, or until no appreciable change in viscosity occurs as determined from pilot samples; after this period the equilibrium viscosities of the test solutions are carefully measured. After correcting these values to the equilibrium viscosities corresponding to the exact total solids content desired in each series of solutions, the results are plotted on an auxiliary chart against percentage composition of the thinner mixture. This auxiliary chart, termed the "equilibrium viscosity diagram," is often useful in connection with the formulation of lacquers as well as the phase diagram which, in part, is derived from it. By means of the equilibrium viscosity diagram one may read or estimate the actual viscosities of solutions of any solids content in any mixture of the solvent and diluent under consideration.
%OF90%BUTYL ACETATEINTHINNER- BY WT.
FIGURE 15. EQUILIBRIUM VISCOSITY DIAGRAM OF NITROCELLULOSE IN 90 PER CENTBUTYL ACETATE-TOLUENE MIXTURES AT 20 O C.
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FIGURE16. PHASHDIAGRAM OF NITROCELLULOSE IN 90 PER CHINT BUTYL ACETATE-TOLUENE MIXTURES AT 20' C .
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%MLTHYL ISOBUTYL KETONE INTHINNER- BY WT. a hydrocarbon diluent, and the value of the dilution ratio varies with the concentration of nitrocellulose at the end point FIGURE 17. EQUILIBRIUM VISCOSITY DIAGRAM of this titration. The curve representing the dependence of OF KITROCELLULOSE IN METHYLISOBUTYL MIXTURESAT 20" C. KETONE-TOLUENE dilution ratio upon the solids content at the end point can be drawn, therefore, on a chart bounded by coordinate axes; one axis representing solids content and the other, the relative proportions of solvent and diluent in the system. The character of solutions of nitrocellulose in mixtures of solvent and diluent is likewise dependent on the concentration of nitrocellulose in solution and the proportion of solvent and diluent in the thinner. Accordingly, these relations can be represented on a chart bounded by the same axes as are required for the dilution ratio relations. The combination of these curves on a single chart constitutes the phase diagram. I n the preparation of the charts, the dilution ratio and viscosity data are taken independently IO EO 30 40 50 60 70 80 90 100 on separate samples. From the dilution ratio 46 METHYL ISOBUTYL KETONE IN THINNER BY WT. data, which are taken by standard methods ( I @ , the "precipitation line" may be drawn on the FIGURE18. PHASEDIAGRAM OF NITROCELLULOSE IN METHYL ISOBUTYL phase diagram. KETONE-TOLUENE MIXTURES AT 20" C.
-
FHBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
A second set of solutions is prepared meanwhile in order to locate the “gel line,” which divides the compositions representing solutions that flow from those that do not flow. For this purpose several solutions are made up to the same solids content, while the liquid composition of each differs but slightly from the composition that preliminary experiments I40
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201
a considerable variation in thinner composition is made. I n general, the former corresponds to the region of plastic flow (3) and the latter to the region of viscous or normal flow. Since we are not principally concerned with the actual values of the viscosities, but rather with the phase relations of the system as a whole, we may eliminate viscosity and plot the compositions represented by the points of maximum curvature, as shown on the auxiliary chart, against solids content. These are the coordinates of the phase diagram, and the system is now completely defined. The phase diagram method of solvent evaluation obviously gives a more complete picture of the solvent characteristics of a solvent than either the dilution ratio method outlined in the first section or the viscosity of solutions made with undiluted solvents studied in the second section. From the phase diagram one can obtain the dilution ratio not only a t 8 per cent solids content, but a t any other concentration of solids a t the end point. The slope of the “precipitation line” indicates how rapidly the tolerance of solvent for diluent varies as the solids content is increased or decreased. Considering the phase diagram as representing all compositions of nitrocellulose, solvent, and diluent, it is clear that the precipitation line separates these compositions into a region within which all mixtures of solvent and diluent will dissolve the nitrocellulose and a region in which the nitrocellulose is not soluble. This much information is not sufficient, however, because even if the nitrocellulose is dispersed, the solution is of little use commercially unless it will flow. The gel line serves to separate the region in which the solutions will flow from those in which they are immobile a t the temperature indicated. The gel line thus indicates the maximum solids concentration that can be used for any proportion of solvent and diluent in the thinner. Even with this additional information the formulator may not be satisfied, for he may be concerned with the optimum conditions favorable to a smooth-flowing film of lacquer. For this purpose a composition on or under the line which limits the region of viscous flow must be selected. A comparison of Figures 16 and 20 illustrates the use of the phase diagram as an aid to formulating. For example, the thinner composition most favorable t o a freely flowing lacquer composed of nitrocellulose dissolved in a mixture of Cellosolve and toluene occurs when the Cellosolve constitutes about 45 per cent (by weight) of the thinner mixture. With such a thinner
have indicated should be near the gel point. One of these solutions will probably be sufficiently close to the gel point so that the composition a t that point can be defined. A sufficient number of gel points are determined a t different solids contents to enable a smooth curve connecting them t o be drawn on the phase diagram. Inspection of the curves on the auxiliary chart on which equilibrium viscosities are plotted against thinner composition discloses t h a t they rise asymptotically to an infinite viscosity as the solvent portion of the thinner diminishes to some definite value. Infinite vis50 cosity is, of course, a gel, and the exact composition of the thinner mixture a t this point can be 40 read from the gel line which has already been located. Inspection of the equilibrium viscosity 3 curves further discloses either that they assume 30 a form somewhat suggestive of a rectangular hyt perbola, or, as in the case of the two-type solvents such as the Cellosolves, that they pass 20 through minima and show a viscosity increase again as the proportion of solvent in the thinner IO mixtures rises t o 100 per cent. FLUID RLOION The points of maximum curvature of the rectangular curves in the normal case and of 0 both halves of the U-curves in the case of the two0 IO 20 30 40 50 60 70 80 90 100 D/. CELLOSOLVL I N THINNER ev WT. type solvents are significant; and when they canFIGURE 20. PHASE DIAGRAM OF NITROCELLULOSE IN CELLOSOLVE-TOLUENE not be determined by inspection, it may be deMIXTURESAT 20” C . sirable to find the mathematical equations of the curves and locate these points by calculation. the solutions remain in the fluid region a t all solids contents The line connecting the points of maximum curvature may up to nearly 15 per cent. With n-butyl acetate, however, be thought of as separating the solutions into two regions as the most favorable composition is the undiluted solvent. regards viscosity behavior. I n one region great changes in viscosity result from slight changes in thinner composition; Therefore, the formulator should try to adjust his thinner in the other region, only slight changes in viscosity result when mixture of Cellosolve and toluene so that it will approach the
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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FIGURE 23. EQUILIBRIUM VISCOSITY DIAGRAM OF NITROCELLULOSE IN 60 PERCENT ETHYL ACETATE-TOLUENE MIXTURESAT 20' C.
optimum composition during evaporation as the drying film Passes from the sol to the gel stage. With the ester solvents, on the other hand, it appears that to realize the best conditions for smooth flow-out, the diluent should leave the film first. It is understood, of course, that these relatively simple relations are greatly complicated by the presence of additional liquid components in the lacquers as well as by solid components in solution and in suspension. Therefore, it is not intended that too much emphasis be placed on the value of these charts as a direct aid to formulating, although the relations brought out in this type of study are thought to be of considerable indirect value. Equilibrium viscosity diagrams and phase diagrams of several lacquer solvents in commercial purity are presented
in Figures 13 to 20, inclusive. For the sake of simplicity in the preparation of these diagrams, dry nitrocellulose was used throughout, so that advantage has not been taken of the coupling effect of the alcohol ordinarily present in nitrocellulose as it is used commercially. This type of study can be extended to include a fourth variable, such as the proportion of solvent to coupler in the solvent portion of the thinner, by plotting this ratio in the third dimension. The resulting solid figure is rather difficult to visualize, however, and practically impossible to draw. Therefore, only two additional pairs of diagrams are presented, Figures 21 to 24, comparing pure ethyl acetate with 60 per cent ethyl acetateethanol in mixture with toluene. Figure 14, which gives the phase relations involving ethyl acetate of 85 per cent ester, may be compared with Figures 22 and 24. Within the limits studied, the effect of additional coupler is to shift the precipitation line slightly towards a leaner, thinner composition and to raise the gel line appreciably,
Summary 1. A system for the complete evaluation of the solvent characteristics of lacquer solvents is presented whereby data obtained by both dilution ratio and viscosity methods are combined on a single phase diagram. 2. Phase diagrams for four lacquer solvents in commercial purity are presented.
FEBRUARY, 1938
INDUSTRIAL AND ENGINEEIiING CHEMISTRY
3. The change in phase relations occasioned by variation in the ratio of ester to alcohol in a four-component system involving nitrocellulose, ethyl acetate, ethanol, and toluene is depicted by a comparison of the separate-plane phase diagrams prepared from pure ethyl acetate, the 85 per cent ester grade, and a mixture containing 60 per cent ester and 40 per cent ethanol.
Acknowledgment The author takes pleasure in acknowledging his indebtedness to C. 0. Strother who was instrumental in developing the phase diagram method of solvent evaluation in this laboratory, and likewise the assistance of his associates, R. A. Briggs, G. R. Penn, and R. W. Callard in the preparation of the material presented in this paper.
Literature Cited Atsuki and Ishiwara, Caoutchouc & gutta-percha, 28, 15,462-4 (1930). Baker, S. Chem. Soc., 103, 1653-75 (1913). Bingham, E . C., “Fluidity and Plasticity,” New York, McGrawHill Book Co., 1922. ENG.CHEM.,19, 968 (1927). Brown and Bogin, IND. Brunkow, Ibid., 22, 178 (1930).
203
(6) Calvcrt, Ibid., 21, 213-15 (1929). (7) Davidson, Ibid., 18, 670 (1926). (8) Davidson and Reid, Ihid., 19, 977 (1927). (9) Ibid., 20, 200 (1928). (10) Desparmet, C u i r tech., 16, 217-25 (1927). (11) Doolittle, IND. ENG.CHEM., 27, 1169-79 (1935). 112) Doolittle, Smith, and Penn, P a i n t , Oil Chem. Rev.,99, 26-8, 48-9 (1937). (13) Frazier and Reid, IND. ENG.CHEM.,22, 607 (1930). I 14) Gibson and McCall, S. SOC. Chem. I n d . , 39, 172-6T (1920). (15) Hatschek, Emil, “Viscosity of Liquids,” London, Bell and Sons, 1928. (16) Highfield, Trans. Faraday Soc., 22, 57-81 (1926). ENG.CHEX, 17, 505 (1925). (17) Keyes, IND. (18) Ibid., 17, 558-67 (1925). (19) McBain, S. Phys. Chem., 30, 239-47 (1926). (20) McBain, Grant, and Smith, Ibid., 38, 1217-31 (1934). (21) McBain, Harvey, and Smith, Ibid., 30,312-52 (1926). (22) Mardles, J. SOC.Chem. Ind., 42, 127-361’; 207-llT (1923). (23) Masson and McCall, J . Chem. Soc., 117, 819-23 (1920). (24) Park and Hofmann, IND. ENQ.CHEW,24, 132 (1932). (25) Park and Hopkins, Ibid., 22, 826 (1930). (26) Schwarz, Caoutchouc & gutta-percha, 12, 3859-60 (1914). (27) Sproxton, Brit. Assoc. Advancement Science, Third Colloid Rept., pp. 82-9 (1920). (28) Sproxton, T r a n s . Faradau SOC.,16, Appendix, 78 (1921). (29) Wilson, IND.ENG.CHEM.,21, 592 (1929).
RECEIVED December 13, 1937.
Hydration of Propylene under Pressure Isopropanol of high strength was produced by the direct high-pressure hydration of propylene gas with water in the presence of dilute phosphoric acid catalyst. The investigation was studied over a range of 95 to 503 atmospheres pressure and of 160” t o 290” C. The equilibrium was determined over this range of conditions, and the following free-energy equations were obtained for the formation of alcohol : liquid phase AF” = 23.25 Tv vapor phase A€’ = 34.7 Toc.
- 3005 - 2530
Under favorable conditions of operation, liquid-phase concentrations may reach 200
D
EVELOPMENTS in petroleum technology to produce high antiknock fuels have left refineries overburdened with large quantities of gas of high olefin content. When it is realized that slightly less than two million barrels of oil are cracked daily to produce in excess of one billion cubic feet Of gas containing from to 23 per cent (3, 6 , 11) and 5 to 18 per cent propylene (3, 6, 11), the im-
FRANK M. MAJEWSKI‘ A N D L. F. MAREK2 Massachusetts Institute of Technology, Cambridge, Mass.
grams of isopropanol per liter of alcohol solution, and vapor-phase concentrations as high as 700 grams per liter of condensate. The concentrations of alcohol formed in both liquid and vapor phases increased as the pressure increased and the temperature decreased. The rate of reaction was very rapid a t temperatures above 240” C. Of the two possible alcohols, only the is0 comppund was present. In addition to isopropanol, isopropyl ether and polymer were formed as byproducts a t the higher temperatures and pressures. The boiling range of the polymer changed markedly as the pressure, temperature, and reaction time increased.
portance of refinery gas utilization is more appreciated. To date, considerable research has been done in this direction; much of it has been successfully culminated into industrial processes with which we are all familiar. In the present case attention has been focused on the utilization of propylene. 1 2
Present address, R6hm & Haas Company, Philadelphia, Pa. Present actdress, Arthur D. Little, Inc.. Cambridge, Mass.
