2520
INDUSTRIAL AND ENGINEERING CHEMISTRY ACKNOWLEDGMENT
This paper is a contribution fro1n American Petroleurn Institute Research Project 37 located a t the California Institute of Technology. Betty KendaII, Virginia Berry, and F'rederic Selleck assisted with the preparation of the data. Elwood Rogers was responsible for :t part of the experimental measurements. LITERATURE CITED
(1) Bridgeman, 0.C., J . Am. Chem. SOC.,49,1174-83 (1927). (2) Caubet, F..2. p h y s i k . Chem., 40,257-367 (1902). (3) Kuenen, 3. P., Phil. Mag., (5)44, 174-99 (1897). (4) Kuenen, J. P., 2.phyaik. Chem., 24,667-96(1897). (5) Kuenen, J. P., and RobRon, W. G., Phil. Mag., (6) 4, 116-32 (1902). (6) Michels, A., and Michela, C., Proc. R o y . SOC. (London), A153, 201-14 (1935).
Vol. 43, No. 11
R. H.,R e a m e r , H. H., Sage, B. H., and Lacey, M'. N.. IND.E,No.CHEM.,41,474-84 (1949). (8) Poettmann, F.H,, and Kata, D. L., Ibid., 37,847-53 (1945). (9) Reamer, H.H.,Olds, R. H., Sage, B. H., and Lacey, W. N., (7) Olds,
Ibid., 36,88-90 (1944).
~tion Inst.,~Washington, ; H.,D.andC.,Lacey, ~ waN.,~Am, Dooumenta; ~ Documenf 3264 (1951).
(12) Reamer,
H.H:, Sage, B. H., and Lacey, W. N., IND. ENQ. CHEM.,41,482-4 (1949). (13) Sage, B. H., and Lacey, W. N., Trans. Am. Zmt. Minine Met. Engrs., 136, 136-57 (1940).
RECEIVED M a y 7 , 1951. For material supplementary t o this article, order Document 3264 from the American Documentation Institute. 1719 N St., N.W., Washington 6, D. C . , remitting $1.00 for microfilm (images 1 inch high on standard 35,mm. motion picture film) or $4.35 for photocopies (6 X 8 inches) readable without optical aid.
Action of Antifoaming Agents at Optimum Concentrations SYDNEY ROSS AND G. J. YOUNG Department of Chemistry, Rensselaer Polytechnic I n s t i t u t e , Troy, N. Y . This work was done as part of an effort to find the mechanisms underlying the action of foam-inhibiting agents. For a comparison of the effects of different agents i t was necessary to find the optimum concentration of each. On this basis the antifoaming effect was compared with the viscosity, the spreading coefficients, and the entering coefficients of each agent for each of two aqueous foaming solutions containing surface-active agents. The sign of the spreading and entering coefficients is usually positive for a foam-inhibiting agent. No precise correlation exists between the magnitudes of the properties here reported, though usually a large positive spreading coefficient and a low viscosity are associated with more effective foam-inhibiting action. Two distinct effects of foam inhibitors could be distinguished. With some, the agent promotes the rate of drainage of liquid from the foam films without much affecting the final thickness of the film at which its rupture takes place. This effect is believed to be the result of a decreased surface viscosity produced by the presence of the agent. Other agents cause the rupture of thick liquid films before drainage of liquid has thinned them to the breaking point. Many agents produce combinations of the two effects.
I
NDUSTRIAL chemists who use antifoaming agents have known for a long time that for most agents there is an optimum concentration, below which it is a less effective antifoam and above which it may actually serve to stabilize the foaming of the system. Hitherto in comparisons of antifoaming agents, a single concentration of each agent, usually 1yo by volume, has been used as interest was chiefly in the existence or nonexistence of antifoaming effect, which, within wide limits, is not affected by variation of concentration of the agent. I t is now established that for insoluble antifoaming agents the answer to that question depends on the sign of the initial spreading and entering coefficients (8, 10). I t now seems of interest to investigate the secondary effect of variation of concentration of the agent. This is of importance
when comparisons are drawn between different agents as it ie more logical to compare optimum effects, a t a concentration for each agent that can be determined only by experiment, than to use the same concentration for each, imposed arbitrarily. By using a variety of agents it is also proposed to elucidate some factors that are of importance in the foam-inhibiting effect. In these experiments only systems that are limited to atmospheric conditions of pressure and temperature are dealt with, and hence any proposed factors or mechanisms of foam-inhibiting action are not held to apply to foams produced in steam generating systems. Gunderson and Denman ( 4 ) have found that use of organic foam inhibitors in steam generating foaming systems is primarily controlled by mechanisms other than those stressed in this paper or in preceding papers of this series. MATERIALS AND METHODS
Two foaming systems were prepared. System A consisted of 0.50% by weight Nacconol NRSF (National Aniline Division, Allied Chemical and Dye Corp.) and 0.75% by weight sodium silicate solution, technical grade (Fisher Scientific Co.) dissolved in distilled water. System B consisted of 0.20% by weight Aerosol OT, 100% pure (American Cyanamid Co.), and 1.00% by weight glycerol, c.P.,dissolved in distilled water. Materials were selected, most of which are commercially available antifoaming agents in current use, an antifoaming agents for these foaming systems. There was little to be gained by using rigorously purified agents as it was not desired to establish effects caused by differences in structure, but to make a more fundamental inquiry-namely, greater precision in the description of the nature of the effect itself. Foaming tests were made on each of the systems A and B alone and with different concentrations of each agent. The measurements were initial foam density, foam stability, viscosity, surface tension, and interfacial tension.
MEASUREMENT OF INITIALFOAM DBNSITY. Two hundred milliliters of sample are put in a 1-liter beaker and the twin blades of a Sunbeam Mixmaster are adjusted so as to come to within less than 1/16 inch from the bottom of the beaker. The whipping is done at the top speed of the Mixmaster. After
INDUSTRIAL A N D ENGINEERING CHEMISTRY
November 1951
exactly 5 minutes a small sample bottle, which has been weighed previously, ia dipped into the beaker near one side, filled with oam, and withdrawn. The top of the withdrawn foam sample ia scooped fist and the sample bottle plus contents is weighed to determine the fo& density. The average deviation of the measurement is about 2%. An alternative methcd of getting foam density has been published I) but, while it is of use for the oil foams for which it is designe it cannot be ap lied to some of the shorter-lived a.suepus fqama that are met in tka work. The initial foam density 1s designated do. MEASUREME~NTB OF FOAM STABILITY. The withdrawal of the sample for the measurement of foam density does not take more than about 10 seconds and is done while the stem is still kept homogeneousby the action of the blades. TheTlades are stopped 5 minutes and 15 seconds after startin The foam is transferred immediately to a 26O-ml. raduated cyfinder, the top of which had been removed flush wit% its hi hest gradation. Thle device eliminated uncertainty and loss o? time in obtaining the roper volume of foam. A stop watch is started durin the trans&ence of the sample and the time noted as each 2 mf. of liquid drains from the foam until no further appreciable drainage is observed.
antifoaming agent, and Y D is the surface tension of the antifoaming agent. The entering coefficient is defined by the expression
EDP = Y F -k
6
(5)
The practical value of this investigation is not to be estiniated by the success or failure in finding suitable antifoaming agents for the foaming systems selected for study. The primary purpose of the investigation is to obtain information about the mechanism of antifoaming action. The selection of systems to study was based on the requirement that they provide copious and stable foam and the foaming test was one that required a quantity of foam still produced despite the presence of the antifoaming agent. No quantitative measurement of foam stability can be made if too little or no foam is formed. Consequently the changes of foam stability caused by the presence of antifoaming agents are examined a t concentrations below that of total foam inhibition. The suitable concentration ranges estend to much higher values than are customarily iequired in industrial practice, probably becausg of the exceptionally stable ind voluminous foam produced by the detergent systenis being studied. The present method of measurement does not permit carrying the Concentration of agents to values where they become very effective antifoams. Where only a little foam is produced the blades of the Mixmaster do not succeed in suspending all the liquid present and the foam cannot be separated from the liquid fast enough to give reliable results for the measurement of stability. The foaming systems alone have LIvalues of about 400 seconds. The reduction of this value by antifoaming agents can be measured by the present method down to about 100 seconds. Foams with lower values are reported merely a8 less than 100 seconds. Not all the agents, even a t high concentrations, can reduce LI even a8 low tts 100 seconds. T h o w that can are
(2)
In these equations g and 1 refer to the volume of gas and liquid in the foam a t time 1, the original volumes being 8. and I,. Measurement of L, is done in a similar way to that described for Lz. Observations are made at the foam-air interface to determine L, and a t the liquid-foam interface to determine Li. A third index, Lj, the average lifetime of 1 ml. of foam, lies between the values of LIand L,. It is obtained from the equation
+ d4Li - Lo)
(3) The values of all these numerical indexes are determined in the present work. It has previously been customary to refer to all three indexes, Li, A,, and Lj as units of foam stability. Apart from the practical inconvenience of using three separate numbers, there are semantic difTiculties produced by using a single phrase to describe three different processes. Of the three, only LJ can be properly called a unit of foam stability, as it actually is a measure of the time that 1ml. of foam-i.e., the mixture of the phases, not either one separately-has an existence of its own. The remaining two indexes, LI and L,, give an approximate account of the relative parts played in the total instability of the foam by drainage of liquid from the foam film and rupture of the films to release gas, respectively. They give an approximate account only as these two factors are not measured in complete isolation even by this ingenious expedient. SURFACE AND INTERFACIAL TENSIONS. Surface and interfacial tensions were meaaured using the Cenco-du Nouy precision form tensiometer and the Cenco-du Nouy interfacial tensiometer, using the ring corrections of Harkins and Jordan (6). The surface and interfacial tensions are used to calculate the initial spreading coefficient and the initial entering coefficient of every agent on each of the two foaming systems. The initial spreading coefficient is defined by the expression
-
- YD
EXYEHIMENTAL RESULTS
Lt is the average time that 1 ml. of liquid remains in the foam (I). The average deviation of the measurement is 2%. Another fundamental numerical index, L,,described as the average time that 1 ml. of gas remains in the foam, is defmed by the equation
G.E. 81066, a methvl silicone oil plus silica aero 1, which gives 100% foam inhibition a t a concentration of 0.5E,though even a t 0.025% concentration it has an estimated 85% foam inhibition (S stem B). Tributyl piosphate in both system has a value of Lc less than 100 seconds a t concentrations greater than 2% in the Aerosol OT foamin system, and at concentrations greater than 5% in the Nacconol AR system. Nonyl Cellosolve in the Nacconol system has a value of Lt less than 100 seconds a t a concentration greater than 4%.
-
8BF = 7 P 7D'F' TD (4) where Y P is the surface tension of the foaming system, Y ~ J is the interfacial tension between the foaming solution and the
YD'F'
These spreading and entering coefficients change as time passes and the two liquids become mutually saturated. For that reason the initial coefficients are calculated from measurements made on the two liquids separately. Occasionally further nieasurementa are made after the liquids have been mixed together and coefficients calculated from these measurements are described as semi-initial and, after equilibrium is reached, final. VISCOSITIES. Viscosities were measured using appropriate Bires of the Ostwald-Cannon-Fenske viscosity pipet (8). The' densities of the liquids were measured on a Westphal specific gravity balance and used for the ring corrections and to convert the viscosity measurements into units of kinematic viscosity. The glassware was cleaned with an acid cleaning solution, rinsed thoroughly, and steamed for 1 hour before being used in the measuremerit of surface tension, interfacial tension, and viscosity. All measurements were made a t 25' C. in a basement room that remained within 1' C. of that figure during the course of the experimental work.
These observations are plotted on linear graph paper as the volume of liquid in the foam versus time. The function ia integrated graphically, using a polar planimeter, to obtain a numerical index, Lz,defined by the equation , rzo
L/ = L,
2521
V
Values of the index LIand of initial foam density, do, for a range of concentrations of various agenta added to Systems A and B are reported in Tables I and 11. These data usually show a minimum in the LIu.3. concentration curve, whieh for the most effective agenta may dip a8 low aa zero foam stability. The
2522
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 11
The data for the calculations are shown in Tables 111 and IV. To make the magnitude of the antifoaming effect more readily understood the last columns of these tables contain the difference between Lj of the foaming System A or B and Lj of the system containing the optimum concentration of each agent. This difference is expressed as a percentage of the foam stability without any additive, and it is therefore called the per cent foam inhibition. These columns give a quantitative comparison of the TABLEI. EFFECTOF VARYINGCONCENTRATION OF ANTILI, AND INIT~AL FOAM antifoaming action of the different agents a t their optimum conF O A ~ N Q AQENT ON FOAM STABILITY, DENSITY, do centrations. (Solution containing 0.50% Nacconol NRSF and 0.757 aodiuni silicate. Tables F' and V I repeat the per cent foam inhibition and Ll = 348 seconds, d o = 0.221 gram per m!). compare it, in successive columns, with the initial spreading Concentration, L1. coefficient, the initial entering coefficient, and the kinematic do, Seconds Gram/MI. % viscosity of each additive. Some agents that were tested in235 0.226 2 . 0 0 A ent 2 creased the foam stability. They are included in the tables for 0.223 190 3.00 dethylisobutylcarbinol 0,222 165 4.00 (CHa)rCHCHgCH(OH)CHa the record. 140 0.214 5.00 0,212 135 6.00 Any evaluation of the relative effectiveness of antifoaming 0.212 140 7.00 agents on the basis of these reported results must be modified 335 0.224 Agent 3 0.50 by the large effect that the presence of a dispersing agent may 215 0.224 Non 1 Cellosolve 1.00 155 0.235 [(C&zCHCHn]rCHOCzH+OH 2.00 have on the property of an agent. In this study, except for the 0.240 120 3.00 two agents, G.E.81066 and Foamicide A, that had dispersing 110 0.257 4.00 < 100 >4.00 initial foam density, do, does not show as great a difference in value on addition of a defoaming agent; it must, of course, tend to increase toward the density of the liquid itself for a foam stability tending to zero, yet the foam stability can be greatly reduced without the initial foam density showing much change.
Agent 5
3 He tanol
~H~'H,CH(OH)C,H~
tsnt
e t'I 1 Celloaolve & H , 8 J ( C 4Hv)OCzHdOH
Agent % Tributyl hosphate (CIH~O)$: 0
0.40 0.75 1.00 1.50 2.00 3.00 4.00 5.00
295 265 255 260 255 265 290 270
0.222 0.220 0.217 0.226 0,226 0.230 0 232 0.235
0.50 1.oo 2.00 3.00 4.00 5.00
315 280 210 170 140 140
0,229 0,228 0.221 0.212 0.205 0.199
0.50 1.00 1.50 1.75 2.00 2.50 3.00
330 310 260 260 275 315 390
0.225 0.219 0.222 0.227 0.219 0.225 0,236
*etnhtykobutyloarbinol
2.00 3.00 4.00 5.00
175 110 95 110 < 100
0.210 0.224 0.225 0.226
0.40 1.oo 2.00 4.00 6.00 7 .oo 8.00
340 345 360 460 530 560
0.221 0.225 0.226 0.231 0.232
1.00 2.00 3.00 4.00 5.00 6.00
300 290 275 260 260 260
0.2L1 0.227 0.230 0.234 0.232 0.235
>5.00
Agent 11 Tetradeoanol CIH~CH(CVH~)CZHI(OH)CH~CH(CHde
Agent 12 Nopco 1600-B Sulfated 8perm oil (7)
550
0.50 340 390 1.00 400 2.00 ~ , ~ - ( ~ ~ ~ ~ - C ~ H I ~ ) ~ C ~ 3~. 0~0 O C I 410 ~ O H 440 4.00 430 5.00
Agent 13 Foamioide L 10070 Di-lwl-amyl henox ethanol
Agent 14 Foamicide A 3 0 7 Di-fed-amylphenoxyethanof plus dispersing agents
0.50 1.00 2.00 3.00 4.00
350 340 340 335 360
TABLE11. EFFECTOF VARYINGCONCENTRATION OF
%
Agent 1 G.E. 8,1000, methyl ailicone oil plua silica aeroge
0.231 0.230 0.229 0.226 0.224 0,222 0.224 0.226 0,226 0.232 0.232
T o avoid unduly increasing the number of measurements, the second index, Lo, was determined for only one concentration of each additive-namely, the concentration a t which LI had been found to be a minimum. With LJ,Lo, and do known for that concentration, the foam stability, L/,could be calculated by Equation 3. By referring to this concentration as optimum for its defoaming action, it is assumed that the minimum in the LJv8. concentration curve is a t the same concentration as that in the LI u8. concentration curve. A large number of experiments have shown that this assumption is not far from the truth.
Li
do
50 0
0.216
1.00 2.00 2.50 3.00 4.00 5.00 7.00 9.00
360 315 180 140 150 160 170 180
0.222 0.224 0.210 0.212 0.221 0.221 0.226
Agent 4 Diisobutylcarbinol [(CHa)&HCHs]zCHOH
1.00 1.50 2.00 3.00 4.00
290 285 265 275 280
0.226 0.224 0 222 0.226 0.229
Agent 5 3-Heptanol
0.50 1.00 2.00 4.00 6.00 8.00
355 290 280 290 290 280
0.224 0.221 0.224 0.228 0.232 0.230
Agent 6 2 6 fLTrimethylnonano1 ~E~~CH(C C H ~: C H ( O HCH,CH(CH~)CH)~CH(CHI)C$~
0.50 1.00 2.00 3.00 5.00 7.00 9.00
360 360 400 435 486 580 626
0.218 0.216 0.224 0.225 0.228 0.239 0.238
A ent 8 3-fIeptyl carbitol
1.00 2.00 4.00 6.00 8.00
385 320 245 210
Agent 9 Tributyl phosphate
1
.oo
2.00 22.00
0.206
#
215
0.230 0.228 0.220 0.218 0.218
210 255
0.288 0.288
< 101)
Agent 10 Silicone oil, no dispersing agent added
0.50 1.00 3.00 5.00
39u 390
370
480,
0.220 0.222 0.224 0.232
Agent 11 Tetradecano
0.50
3.00 5.00
440 475 545 GOO
0.221 0.222 0.224 0.232
Agent 15 Terposol No. 3 Various terpenrl ethers
0.50 1.00 2.00 4.00 6.00
370 410 415 385 390
0.221 0.230 0.230 0.231 0.231
Agent 16 Uoon lubricant LB 1146 Polyalkyleneglyool derivative
0.50 1.00 2.00 4.00 6.00
400 400 420 465 670
0.225 0.224 0.234 0.231 0.239
1.oo
402
8eoO6ds GramjMl.
0.025 0 50
0,236 0.242
-
ANTIFOAMINQ AQENTON LI and do
(Solution containing 0.20% Aerosol OT and 1.00% glycerol. seconds, do = 0.223 gram per ml.) Concentration, Li
November 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE111. FOAM STABILITXBS
(Solution oontaining 0.50% Naooonol NRSF and 0.767 aodiam silioste at the optimum ooncentrationa of vanow antifoam& agents) 0 timum Foam d'onoenInhitration, LI Lo, LI bition, No. Agent % ' Beco~dmLconds b o o & % 1 G.E. 81066 0.50 0 0 100 0 2 Mebh lisobutylcarbinol 6.00 135 90 180 170 Nonvr Cellosolve 3 4.00 82 110 305 375 5 3-Heptanol 1.00 255 540 69 595 7 3-Heptyl Cellosolve 71 140 5.00 510 600 3 - H e ~ t v lCarbitol 58 8 1.50 260 715 845 Tributyl phosphate 9 4.00 95 1060 51 848 Tetradeoanol 44 11 0.40 1130 340 965 12 Nopoo 1600-B 5.00 260 1480 1180 31 13 Fosmioide L 0.50 340 1340 22 1040 14 Foamioide A 3.00 335 1215 29 1470 No agent 0 350 1720 2080
TABLE IV. FOAM STABILITIES (Solution containing 0.20% Aeroso! OT and 1.00% glycerol at optimuni concentrations of various antifoaming agents) 0 timum Foam EbncenInhitration, LZ Lv L/ bition, No. Agent % Seoohda 8eooLds Secohds % 1 G.E. 81006 0.50 0 0 0 100 2 140 210 Meth lisobut lcarbinol 3.00 230 88 Diiao
