INDUSTRIAL A.VB ENGINEERIh7G CHEMISTRY
November, 1925
1117
Ethylene Glycol' A Contribution of Chemistry t o the Automobile Antifreeze Problem By G. 0. Curme, Jr. and C. 0. Young CARBIDC
function in winter weather and to take the place, during "le months when Ing 'Veather is expected' of the pure water used during the nonfreezing months. Current trends in design
conclus-
h
C . + R l J O N ClIEArICALS C O R F . , LOKG I S L A Y D
1
Received September 24, 1925.
s.Y .
As a result of an extended period of research and development, ethylene glycol is now being produced in large quantity and by methods which will permit of indefinite expansion. The value of ethylene glycol as an automobile antifreeze material will be thoroughly appreciated when its remarkable properties become better known. By combining the qualities of both alcohol and glycerol, ethylene glycol is able to satisfy the most exacting requirements for an antifreeze material. I t affords positive protection against freezing, is not corrosive or harmful to the engine or radiator, and does not lose its effectiveness through vaporization or decomposition. Moreover, it is odorless, free from solvent action or lacquer or varnish finishes, and permits efficient motor operation under all conditions.
ively that the water-cooled type Of engine is practically the survivor after years Of study On types' and further that the body sty1es represent an insistence O n yearround usage irrespective of weather conditions' these two conditions fixed and with the current estimates of a p p r o x i m a t e l y nineteen million automobiles of all classes in use at the present time, it is a challenge to the chemist to discover and to the chemical manufacturer to produce a t reasonable cost a satisfactory nonfreezing, cooling medium to meet the specifications of the automotive engineer, I n the earliest days of the automobile this same need was felt and many suggestions mere offered, but few materials were found to be even approximately satisfactory. It was early discovered that since the cooling system is designed for the use of water, which possesses a n unusually high specific heat, practically all liquids other than water solutions were unsuitable. This eliminated, or restricted to limited use, all organic liquids not miscible with water, such as petroleum fractions. Another effort was made in the direction of using salt solutions, but here the variety of metals used in the cooling system introduced peculiar corrosion difficulties which proved the unsatisfactoriness of all save nonelectrolytes. Ethyl alcohol was among the materials first tried, and it alone has given results approaching general satisfaction, as may be seen from the statistics of consumption, which show approximately 28,000,000gallons consumed in the United States for this purpose in the season of 1924-25. More recently glycerol has been suggested and it too has been found suitable in some respects. Accurate tests, however, have shown that glycerol is not the ideal material for this use and further, since it is a by-product, its production cannot be increased to affect more than slightly the total requirements for antifreeze solutions. ,
CITY,
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lose its nonfreezing properties during and after continued use. terlally The material change shall the not boiling mapoint of water when dissolved
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in it.
To these general specifications could well be added: The material should not attack automobilefinishes, it should be odorless, it should be noninflammable; its water solutions should have a low v i s c o s i t y ; its water solutions should have high heat capacity.
Shortcomings of Alcohol as an Antifreeze
Since these specifications have been constructed solely from the standpoint of the user, without regard for actual commercial materials available, it is of interest to consider what the relationship is between the desired properties for an antifreeze and those of the best commercial materials in use. I n a recent announcement the Bureau of Standards3pronounced denatured alcohol as of that date (1924) "the best material to keep automobile radiators from freezing." Very obviously, as any chemist knows, alcohol solutions do possess materially different boiling points from that of pure water and also these solutions do lose their nonfreezing properties during continued use through evaporation of the alcohol. As regards odor, inflammability, and destructive effect on certain types of automobile finishes, it also fails to meet the most exacting tests. It may fairly be stated, therefore, that the problem of providing an antifreeze solution, even but approximately close to ideal specifications, is still far from a commercial solution, and the chemist of today may well consider it seriously. I
Success with Ethylene Glycol
I n the course of an extended program of laboratory research, process and factory development, extending over the past ten years, this corporation has produced many new chemical materials, principally in the lower aliphatic series, and has made commercially available others long known in academic circles, but never before available in quantity. Among these materials is ethylene glycol (CH20H.CH20H). I t s properties a t once indicated its value for a use such as that 2
3
Bur. Slondards, Leller Ctrcular 28 (December, 1921). News Release, November 23, 1924,
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1118
of an antifreeze4and extended laboratory tests together with several years actual trial have well demonstrated the early expectations. Furthermore, the manufacturing conditions affecting its production are such that any demand for glycol for antifreeze purposes may be met without disturbing the production of other commodities and at diminishing rather than increasing cost.
Vol. 17, No. 11
except the most severe winter conditions. For the extreme northern parts of the country a 45 per cent solution may be required, but in those regions where the minimum temperature rarely drops below -20.6' C. (-5' F.), a 35 per cent concentration is perfectly satisfactory. The points given on these curves indicate the first formation of ice crystals. Total solidification does not occur until considerably lower temperatures are met, but the solution becomes thick and mushy with decreasing temperature. For satisfactory car operation the formation of ice crystals should be avoided since these tend to clog the system and prevent proper circulation of the cooling medium. However, this spread between initial freezing and solidification is added insurance against damage through rupture of cylinder jacket or radiator. Action on Metals
In a commercial way it might be said that ethylene glycol is a new product, for although it has been known since 1856, its industrial production and development were not undertaken until the last few years. With this quantity production has come a greater appreciation of its possibilities, and an increased utilization as a solvent, intermediate, or moistening agent. But of even greater value appears to be its ability to serve as an antifreeze material for automobile radiators. Ethylene glycol is the first and simplest member of the class of polyhydric alcohols. It is a clear, colorless liquid, boiliig a t 197' C. (387' F.),'odorless, and has a slightly sweetish taste. In structure and characteristics it resembles somewhat both ethyl alcohoI and glycerol and occupies an intermediate position between the two. As a solvent and preservative it approaches ethyl alcohol, while in physical p r o p erties it assumes more the nature of glycerol. It is perfectly soluble in water in all proportions and, of course, is a nonelectrolyte. In this combination of the valuable properties of both alcohol and glycerol lies the chief value of ethylene glycol ae an antifreeze material. Freezing Points of Solutions
Ethylene glycol in aqueous solution depresses the freezing point of the solution in proportion to the concentration present, down to about 60 per cent by volume, which solution freezes a t -49' C. (-56' F.). For higher concentrations the freezing point increases again to -11.6' C. (11.3' F.), that of pure ethylene glycol. The dilute solutions, therefore, are admirably suited for use in automobile radiators, and properly chosen ones will not freeze a t any temperature at which it is desired to operate a car in this country during the winter months. A comparison between the freezing points of solutions of ethylene glycol, ethyl alcohol, and glycerol (Figure 1) shows that less glycol is required to produce a nonfreezing solution a t any given temperature than either alcohol or glycerol. Thus a concentration of 33 to 40 per cent (by volume) of glycol when put in a radiator will insure against anything 4
Hibbcrt, U. S.Patent 1,213,388.
Ethylene glycol, as mentioned above, is a nonelectrolyte and therefore would not be expected to exert any corrosive action on metals or metallic couples. This expectation has been fully justified by an extensive set of laboratory and practical tests. No more evidence of corrosion has ever been noticed with glycol solutions than is obtained with pure water. Upon rubber hose connections a slight softening and swelling is a t first apparent, but no loss of mechanical strength is experienced by the hose. Connections have been used for three winters with no greater deterioration than would normally come during the same period using water alone. Thus it is seen that ethylene glycol satisfies the first major requirement of an antifreeze material. Reasonable concentrations afford positive protection against damage through freezing in any weather encountered by the winter motorist, and these solutions of glycol have no injurious effect upon any part of the motor or radiator. Permanence
Ethylene glycol once introduced into the radiator system,
in aqueous solution, remains there unless it is lost through leakage or is intentionally withdrawn. Furthermore, extended use of these solutions does not alter the ethylene glycol through decomposition or change in structure. These solutions, a t the end of the winter season, unless dissipated through leakage or other mechanical sources of loss, will be fully as effective against freezing as when introduced. Also, if desired, the solutions may be removed a t the close of the season and stored for use the following winter. The principal reason for this extreme permanence of glycol solutions, and the /w 90
80 70
60
30
40 90
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MATER M I X T U R t S
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greatest distinguishable difference between glycol and alcohol solutions, lies in the low vapor pressure of ethylene glycol in dilute aqueous solutions. The glycol possesses such a high boiling point that a t 100' to 105' C. (212' to 220' F.) its vapor pressure is low, and as a result a negligible amount only is lost through vaporization from boiliig aqueous solutions. The vapors from these solutions contain water but
November, 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
no glycol, and as a result the solutions become more concentrated with respect to glycol and possess lower freezing points after extended heating. Addition of water to make up that lost through vaporization restores the solution to its original strength. On the other hand, the vapors arising from boiling solutions of ethyl alcohol contain large percentages of alcohol, and the concentration of the boiling solution quickly drops. When applied to radiator solutions this merely means that antifreeze solutions composed of denatured alcohol are continually becoming weaker as the car is used, with a resulting rise in the freezing point of the solution. The relative amounts of antifreeze contained in the vapors of boiling solutions of alcohol and of glycol mixtures may be seen from the curves of Figure 2. A 78 per cent concentration of ethyl alcohol is found in the vapors of a boiling 40 per cent solution, whereas the concentration of glycol in the vapors of a similar solution of ethylene glycol is too low to be accurately determined.
1119
The most satisfactory car performance is obtained when the formation of ice in the radiator solutions is prevented, and for that reason the concentrations as represented on the freezing point curve are recommended. Since the water evaporates from these solutions rather than the glycol, the mixture slowly becomes more concentrated after use and freezes at still lower temperatures. Addition of more water restores the original concentration. The maximum temperature obtainable in the cylinder block is controlled by the boiling point of the cooling liquid, so that with a 35 per cent glycol solution a maximum temperature of 105' C. (221 O F.) might be expected. This boiling temperature would, of
Maintenance of Optimum Engine Temperature For the most satisfactory operation the cooling system of an automobile should maintain the temperature of the motor a t a temperature slightly below the boiling point of pure water. Temperatures of 79' to 93' C. (175' to 200' F.) are usually recommended by the car manufacturer. The third major requirement of the Bureau of Standard's ideal antifreeze is, therefore, directed toward the maintenance of this optimum engine temperature when it is specified that "the material shall not materially change the boiling point of water when dissolved in it." Solutions of ethylene glycol in the concentrations normally employed as antifreeze mixtures-i. e., up to 40 per cent by volume-boil at temperatures only slightly higher than pure water (Figure 3). Accordingly, machines using glycol solutions in their radiators are able to operate a t their customary
temperatures throughout the winter. The boiling points of alcohol solutions (Figure 3) are very much lower than that of pure water, which results in engine temperatures too low for efficient operation of the car, and excessive vaporization and loss of alcohol as the temperature of the mixture approaches the boiling point. Illustration of Advantages of Ethylene Glycol
A specific example, perhaps, will summarize the results and advantages arising from the use of ethylene glycol antifreeze solutions. A solution of 35 per cent concentration (by volume) will prevent any freezing in the radiator down to temperatures of -20.6' C. (-5" F.), and in addition has a further factor of safety of many degrees before any severe damage through rupture can occur to the engine or radiator.
%
GLYCOL BY
VOLUME
course, be an extreme case, and usually a condition closely approaching summer operation is found. In the event that some of the glycol solution is lost, through leakage or spillage, the quantity of material necessary to restore the original 35 per cent solution may easily be determined by the aid of an accurate hydrometer and reference to the gravity chart of ethylene glycol solutions (Figure 4). Other Advantages I n addition to fulfilling the three general specifications for a satisfactory antifreeze material, ethylene glycol possesses other characteristics which further emphasize its qualifications for this purpose. Among these may be mentioned the relatively high heat capacity and low viscosity of its solutions, its odorless and noninflammable nature, and the absence of any solvent action on lacquer or varnish finishes. Although pure ethylene glycol is considerably more viscous than water or alcohol, its aqueous solutions of the concentrations normally used for antifreeze purposes differ only slightly from water a t the operating temperatures of the engine and radiator-a point of very great importance in permitting unretarded heat transfer from engine wall to liquid and from liquid through the radiator tubes to the air. Also, a comparison of the heat capacities per unit volume of solutions of glycol, alcohol, and glycerol shows that all three of these materials are substantially equal in this respect. The resulting effect, therefore,'as far as the proper cooling of the engine is concerned, is virtually the same whether water or glycol solutions are employed. This has been demonstrated in several cases by the continued use of glycol solutions in cars well up into the summer months. The complete freedom from the disagreeable odors always attending the use of ordinary denatured alcohol, together with the noninflammability of ethylene glycol is an additional recommendation for its use. Several cases have been recorded where alcohol vapors arising from heated radiators have been carelessly ignited, with unpleasant and even disastrous results, and it is not uncommon in winter to notice the odor of denaturants so strong in crowded streets or in closed cars as to be decidedly obnoxious. One consideration which will demand more attention with the universal usage of nitrocellulose lacquers for body finishes is the solvent action of antifreeze solutions on these finishes. Ethylene glycol, itself or in solution, is harmless to these lacquers, and will cause no damage if spilled on the radiator or hood. Denatured alcohol, on the other hand, possesses decided solvent action, and unless this is realized and psr+:--
INDUSTRIAL AND ENGINEERING CHEMISTRY
1120
lar care taken to avoid contact between the alcohol and the finish, trouble may be experienced. Such damage will be difficult to eliminate where it is necessary at intervals to add more alcohol to the radiator throughout the winter months, or where a stream or vapors rich in alcohol flow back over the hood when the car is in motion. Conclusion
In any study of the antifreeze problem such as given above, the apparent simplicity of the requirements is the striking feature. That these requirements have not been successfully met, however, in a quarter century of progress is a sufficient warrant for this additional consideration. All problems, however, appear simple as they near solution, and in this case it would seem that the successful combination in
Vol. 17, No. 11
a single chemical compound of all those properties heretofore found valuable for the purpose and the development of processes for producing this material on an indefinitely large scale is the proper key to this long-discussed situation. If this belief is proved by the coming years to be correct, the wideness of potential application of ethylene glycol will mark another success to the credit of the American chemical industry, ranking well with others of the past, that will continue to justify the faith in it so fortunately entertained by the public. Acknowledgment
The authors wish to acknowledge the helpful service rendered by the laboratory of the Linde Air Products Co., Buffalo, S. Y., in preparing the charts used in this paper.
Two-Type Lacquer Solvents'
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By D. B. Keyes
u. s. I N D U S T R I A L ALCOHOLCO.,BALTIMORE,h f D .
I
T IS well known that a combination of ethyl ether and ethyl alcohol is a better solvent for nitrocellulose than either solvent alone. The same is true of a mixture of ethyl alcohol and ethyl acetate. It is therefore natural t o suppose that a single compound having the properties of both an alcohol and an ether or an alcohol and an ester would prove an excellent solvent for nitrocellulose. It has been found in practice that the monoethyl ether of glycol and ethyl lactate, which represent the two-type solvents just mentioned, are very powerful solvents for nitrocellulose. The foregoing combinations, ether-alcohol and esteralcohol, are not the only possibilities. Ketones are also solvents for nitrocellulose, so the most important possible binary combinations are as follows: ester-alcohol, ether-alcohol, ketone-alcohol, ketone-ester, ketone-ether, and ester-ether. These two-type solvents have proved valuable not only as nitrocellulose solvents but also as resin solvents. Ethyl lactate, for example, will dissolve ester-soluble nitrocellulose and alcohol-soluble resins such as shellac. The ideal solvent for lacquers should dissolve both nitrocellulose and resin and hold both in solution in any desired proportion without the addition of further solvents or blending agentsS2 Furthermore, the ideal solvent should produce solutions of nitrocellulose and resins which will withstand the addition of large amounts of nonsolvents such as aromatic hydrocarbons and small amounts of water without the precipitation or separation of any constituent. In view of these facts it has seemed advisable to list the simpler compounds that fall within this two-type group. It will be noticed that only a few of these compounds are now marketed commercially as lacquer solvents. Possibly some of the others will prove to be valuable constituents in the modern wood and automobile lacquers. This list includes not only the two-type solvents which have been tried out in these laboratories, but also others which from theoretical considerations should prove of practical importance, Under each solvent will be given the graphic formula, the boiling point, an indication of how it can be made, and any reference to its use in lacquers. The boiling point is given in order to determine the solvent's position in the boiling point classification.2 1
Received August 11, 1925.
f
THISJOURWAL, 17, 558 (1925).
Ester-Alcohol Solvents Ethyl Glycolate CHtOH
I B. p. 160" C. COOCzH, This solvent can be made by the esterification of glycolic acid with ethyl alcohol. It is an excellent high-boiling solvent for nitrocellulose and many resins. Its use in lacquers together with nitrocellulose, resins, and hydrocarbons has been patented in germ an^.^ Ethyl Lactate CHI I I
CHOH
E.p. 152' C.
COOCzH5 This high-boiling solvent can be made by the ordinary method of esterification of lactic acid with ethyl alcohol. The yield is poor, however, owing t o the formation of lactides. This solvent seems to have distinct alcohol properties, which make i t an excellent solvent for alcohol-soluble resins. It is one of the strongest nitrocellulose solvents on the market a t the present time, and its nitrocellulose solutions will withstand large amounts of diluents such as the hydrocarbons, also nonsolvents such as water.z Gruter has taken out a patent covering a lacquer composition in which ethyl lactate is specifically stated as the primary ~ o l v e n t . ~ Ethyl ( p ) Hydroxypropionate CH20H
I I COOCzHs CHz
B. p. 187" C.
This high-boiling solvent has been made only on an experimental scale by esterification of the corresponding acid. No simple method of synthesizing this acid has been published as yet, but if such a method would be found this ester-alcohol would undoubtedly have solvent properties similar t o ethyl lactate. Triethyl Citrate CHz-COOCzH5 HO-A-~)OOCZH~
I
B. p. 261 "-3 C. (300 mm.) O
CHr-COOCzH5 Byke-Guldenwerke Chemische Fahrik, German Patent 381,413 (January 24, 1913). 4 U.S. Patent 1,195,673(August 22,1916),owned by Chemical Foundation.
