INVESTIGATION OF
C20
TO
C25
FATTY ALCOHOLS AND
BLENDS AS WATER EVAPORATION RETARDANTS ALEXANDER
J.
SIMKO’
A N D
RUSSELL
G .
DRESSLER
Trinity University, Sun Antonio, Tex. 78212.
Pure samples of the odd and even, saturated CZOto CW fatty alcohols were prepared and tested, individually and in blends, to determine their efficiency as water evaporation suppressants. The peculiar characteristics of the alcohols and their blends appear to fit no standard pattern and mixtures of closely related alcohols can be much more effective than either component separately. The linear relationship existing in the C13 to CZOalcohols does not continue into the longer-chain alcohols. Maximum efficiency results from simple ratio proportions in the binary mixtures tested, indicating a definite packing arrangement of the molecules in the monolayers. Efficiencies were higher ( u p to 86% saving in evaporation) than attained by previous workers. The economic implications of the appreciable water savings secured in this study are discussed.
THEsaturated fatty alcohols continue to be of interest both theoretically and practically in their role as surface monolayer film retardants in water evaporation. Of the organic chemicals tested, these materials have been found by many researchers to be among the best for this purpose. Noe and Dressler (1967) investigated pure, odd and even saturated alcohols of carbon numbers C13to Czn used individually and found that water evaporation savings within that carbon number range increased lineally with carbon chain length (Figure 1). Foulds and Dressler (1968) studied saturated alcohols of carbon numbers 14 to 20 used as binary or trinary blends. Certain mixtures of even and odd alcohols gave extraordinarily high evaporation retardation efficiencies, appreciably above those of the pure materials. The combination of CISwith Czoalcohol (both materials of normal and saturated structure) had been given special attention. mole ratio of C19 and Cz0 (Figure 2 ) . However, mixtures of even with even or odd with odd carbon number alcohols gave no enhancement over the pure materials. Present Study
This present study represents an attempt to explore the various alcohol blends further, especially those in the higher range (CzotoG5), where it was expected that greater chain lengths might give high efficiencies, as deduced from the Noe and Dressler trend with pure materials. Aside from Foulds’ work, no references could be found relating to the use of mixtures of odd- and even-chained alcohols. Accordingly, in the present work, the objective was to determine which alcohols and which mixtures in the C20 to Czj range appeared most efficient and to see if these effects could be understood and explained. The effectiveness of a monolayer in reducing the rate of evaporation of water depends on two factors: its “spreadability” and the intrinsic resistance of the complete
’ Present address, Jefferson Chemical Co., Inc., Houston, Tex. 446
77052
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
monolayer. Some of the effects in the present study (Figure 6) may be due largely to spreadability rather than to the intrinsic resistance of the film. The use of high carbon number alcohols (above 18) in practical application on outdoor reservoirs has been handicapped by the slow spreading of these alcohols on the water’s surface. However, the blends tested by Foulds and Dressler indicated a faster and more satisfactory rate in some cases. Also, materials such as wetting agents conceivably could be added to reluctant alcohols to achieve more effective spreading performance. Another factor concerning the alcohols with carbon numbers above 18 is their brittleness, affecting their ability to heal a broken film. Under high compression they have a tendency to break. The present work indicates that odd-even mixtures retain more fluidity, avoiding to some extent both of the above deficiencies. Apparatus
The apparatus employed was that used by Jones (1958) and Cheves et al. (1965), as modified by Noe and Foulds. Initially used a t Southwest Research Institute some ten years ago, this assembly permits control of the several factors of importance to the rate of evaporation under field conditions-air velocity, air temperature, relative humidity, and water surface temperature. The apparatus consists of a steel water bath containing the test battery jars with specially designed covers incorporating an air inlet and diffuser to control air velocity. The original apparatus was completed with dehumidified air supply lines, pressure reducers with regulators, drying towers, air flow dividers, needle valve manometers, and a thermoswitch with electrical heating coil. Outage measurements were taken with a micrometer hook gage, reading in 0.001-inch intervals, described by Cheves et al. (1965). Previous Work
Xoe and Dressler (1967) made a systematic study of the retardation efficiencies of the C U to C20 fatty alcohols,
/O
/I
/3
/f
/5
/6
./?
CARBON
/8
/9
CHAIN
20
21
22
23
2t
LENGTH
Figure 1. Effect o f chain length o n p e r cent savings 80 70
60
50
t Z
W
0
e0
30
0
’ 0
1
/o
’
1
1
1
1
1
50 60 70 80 90 /OO FRACTION OF C,,-Czo
20 30 40
MOLE
(cz0)
CARBON CHAIN ALCOHOL Figure 2. Per ceint savings vs. mole f r a c t i o n
the resistance to evaporation but the rate a t which materials spread and form monolayers. Following Noe’s findings, Foulds performed over s k t y 4-hour evaporation tests to determine if a similar performance would be attained with mixtures of those compounds. His results indicated that the mixtures represent a higher level of water evaporation retardation efficiency than Noe found for pure, unmixed fatty alcohols. Such results appear to represent a deviation from LaMer’s statement that long-chain impurities could decrease the efficiency of the film. But, as LaMer pointed out, in certain cases of monolayers with two components there sometimes exist molecular interactions which can increase the evaporation resistance. I n research studies by various investigators at Trinity University over the past nine years, the most efficient evaporation suppressant tested prior to the present work was a mixture of 25% C19 and 75% CZO.Foulds observed that C19and Cl0 mixtures gave a maximum a t the above composition with 79% saving of water in laboratory tests. A high degree of savings was reported by Mihara (1962), achieving 85 to 90% efficiencies, using ethylene oxidefatty alcohol adducts. LaMer and Aylmore (1962) showed the evaporation resistance of mixed monolayers of octadecanol and hexadecanol to be dependent on the composition of the mixture. They surmised that the fact that alcohol mixtures exhibit a resistance higher than either component represented a deviation from idealty caused by impurities in the alcohols used, and that mixtures of pure alcohols exhibit ideal behavior a t all pressures. The results obtained by Foulds, however, indicate that these unexpected variations are the result of unique molecular orientations which reach a maximum at a given composition of the mixed film. Source and Purification of Samples
including the odd-carbon-chain compounds. Prior to that time, the odd-chain alcohols had been largely neglected, partly perhaps because they do not occur naturally and must be produced synthetically. I t had been claimed, however, that they ,are less susceptible to microbial degradation than the (even-chain alcohols (Crawford and Stoops, 1960). This may influence the length of time a water evaporation barrier could be useful and effective under field conditions, assuming that degradation is a major factor of loss as compared with wind drift of the film and other losses. Noe’s work showed further that “odd-carbon-chain alcohols behave similarly to even-carbon-chain alcohols, and that both fit the same straight line in a plot of carbon chain length us. water savings.” I n pioneer studies at Southwest Research Institute, Dressler (1956) had observed that mixtures of alcohols may be somewhat more effective than pure alcohols. For example, a mixture of 80% Clu, 10‘: CIS, and 10% C2” gave slightly higher efficiency in laboratory tests than pure CL6. I n retrospect, this probably was due to the presence of the longer chain alcohol rather than to any synergic effect. The Noe and Dressler studies also confirmed the findings of Rosano and LaMer (1956) that straight-chain alcohols free of double bonds appear to form the best condensed monolayers, and also strengthened the hypothesis that chain length is the most important single parameter of the molecular architecture, in that it controls not only
The alcohols used were analytical grade, obtained from K & K Laboratories, Plainview, iX.J. They were further purified by recrystallization three times from absolute ethanol. The melting points of the purified alcohols were obtained on a Fisher-Johns melting point apparatus (Figure 3). I n general, the melting points agreed within 0.3’C. of handbook values. The alcohols tested were C X 1-heneicosanol, CL2 1-docosanol, C n 1-tricosanol, 1-tetracosanol, and Czj 1-pentacosanol. Number and Accuracy of Test Runs
A total of seventy-three 8-hour evaporation studies was performed during this experimentatidn. The first run on the apparatus was made with commercial 1-octadecanol. This served as a check on procedure and gave an assurance that the apparatus was functional. Over the years this standard reference sample gave consistent test results within the range of 51 to 53%. This test was rerun at regular intervals to check the accuracy of the apparatus. Some of the mixtures tested by Koe and Foulds were also retested to verify the precision of the sample preparation and the apparatus. I n duplication runs on the same specific mixture, the degree of precision obtained was high, within the =tl% deviation in the per cent of efficiency value. This indicates that the apparatus was functioning properly and that the method of application was dependable. The average water loss from the blank (control) jar fluctuated between 0.108 and 0.122 inch of water. The VOL. 8 NO. 4 DECEMBER 1 9 6 9
447
POINT D€TERMINAT/ON
M€iT/NG 8OS
70'
60'
m0
c,
G9
LENGTH
c.20
OF
cZ/
CARBON
'27
cZ3
cZ.?
CHAIN
'35
ALCOHOL
Figure 3. Melting point vs. length of carbon chain alcohol
reason for this variation appeared to be the fluctuation in temperature and humidity of the room in which the tests were performed. This was in line with Foulds' and Noe's work; their average blank results, from their 4-hour runs (0.061 inch) were half of the authors' results from their 8-hour runs. Results of Test Runs
At first, 4-hour test runs were used, as previous investigators had done; later the length of the test runs was increased to 8 hours in an effort to secure more representative readings. The conditions governing these experiments were: Air temperature Water bath temperature Temperature of water in test jar Air flow a t standard conditions Relative humidity of air
30" =k 0.5"C. 300 + 0.20C. 30" =k 0.2" C. 12 + 0.5 liters per minute Less than 5%
