WILLIAM A. HlGGlNS The Lubrizol Corp., Cleveland, Ohio THOMAS J. WALSH Case Institute of Technology, Cleveland, Ohio
Factors in Preparing Bentonite-Stabilized Asp halt Emulsions A novel method of measuring asphalt particle size is helpful in determining effectiveness of emulsification and is the most practical result of the study G M u L s m N s of various bitumens have been prepared for many years and have many uses. A literature survey reveals the wide range of materials and procedures used to emulsify asphalts and coal tar derivatives. Asphalt is a low cost thermoplastic occurri'ng naturally, and as a by-product of the petroleum industry. The properties of this complex organic resin have been studied by many investigators (9, 7 7). Asphalt emulsions are of interest in road treatment for their ease of handling, and claystabilized emulsions as roof coatings for the outstanding weatherability of their dried films. Two general types of asphalt emulsions are-chemical-stabilized, and clay-stabilized. The latter is of interest in this study. Kirschbraun was active in this field and holds several patents (5-8), in which bentonite is used for bituminous dispersions. Clay-stabilized asphalt emulsion has, as the external phase, a hydrated, colloidal clay suspension referred to as a suspension, a slurry, or a slip. This sus-
Figure 1.
pension may contain from 3 to 15 wt. % of clay. Bentonite clay is a hydrous aluminosilicate which forms a viscous, alkaline water suspension. The clay suspension and clay-stabilized emulsions have definite yield points and viscosities which vary with the rate of shear, They both exhibit thixotropic properties. The physical and chemical properties of this mineral have been exhaustively studied (4). The molten asphalt is mechanically dispersed by the shearing action of the mixing equipment and the movement of the hydrated clay particles. Individually designed paddle mixers and a variety of heavy duty agitators have been used to produce the desired dispersion. I n this investigation, a turbo-type mixer, consisting of a centricone affixed to a vertical shaft and suspended in a cylindrical, baffled container, served as the emulsifier. The shearing action was almost entirely due to the internal movement of the suspended clay particles. Two purposes of the investigation are
Internal dimensions of the turbo-emulsifier
-to relate operating variables of the mixer to particle size of the dispersed phase, and to study the effect of heat and chemical treatment of the slurry upon the emulsification process. The ultimate objective was to establish mathematical relationships between the particle size of the internal phase and the energy required to produce the emulsion. Therefore, a rapid and effective method of rating particle size was developed to approach this objective.
Equipment The turbo mixer consisted of a cylinder, 10 inches in diameter and 16 inches in height, in which rotated two vertically suspended centricones, 3 inches in height with minor and major diameters of 3 and 4 inches, respectively (Figure 1). Six 1-inch vertical baffles extended from the container wall. I n this investigation only the lower half of the unit was used. The revolving centricone pum p
Figure 2.
Complete emulsification system
VOL. 49, NO. 8
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1267
2. A Volclay bentonite from the American Colloid Co. This material is 90% mineral montmorillonite. The basic particle is 6470 silicon dioxide, 21y0 aluminum oxide with minor portions of magnesium oxide and ferric oxide. The surface of the basic particle contains adsorbed hydrated cations such as sodium, potassium, and calcium. The base exchange capacity of this material averages 1 meq. per gram. 3. Cleveland city water with a total hardness of 116 p.p.in. 4. A buffer consisting of 8% potassium dichromate and 8Ye acetic acid in water solution. 5. Standard 98Ye concentrated sulfuric acid.
the liquid mass upward adjacent to the baffled wall and down through the hollow cone along the shaft. The shaft was driven by a 3/4-hp. electric motor through a variable speed Reeves drive (Figure 2). The asphalt was maintained at elevated temperature and was delivered to the emulsifier by a Bede circulating paint heater. T h e asphalt lines and pump and the emulsifier walls were heated by resistance elements and insulated with asbestos lagging. The major evaluating instrument was a Spencer haemacytometer or blood-cell counting chamber which contains a ruled grid at the base of a calibrated volume. This chamber, placed upon the stage of a compound microscope, was used to obtain particle size ratings for each experimental emulsion. Other evaluating instruments were a GE volt ammeter and wattmeter, a Sticht tachometer, a Brookfield viscometer, and a Beckman p H meter.
Procedure
The preliminary work established as constants the batch size: the clay-slurry concentration, the asphalt temperature. the chemical treatment of the clay slurry, and the handling techniques. The centricones at maximum rotational speeds of 1600 to 1700 r.p.m. were unable to pump emulsions with asphalt content greater than 40%. Thirty controlled runs were made with 40% asphalt and 3Ye clay content according to the following procedure : 1. The bentonite suspension was prepared a t 10% concentration in the emul-
Materials
The materials used in this investigation were: 1. An air-blown, emulsion-base, petroleum asphalt of 50 to 60 needle penetration from Standard Oil Co. of Ohio.
Table 1. Av. Shaft Speed R.P.M
Amperes 4v. Currenl current rise
Power Factor
1.05
6 8 9 12 16 30
75-122 77-104 79-104 82-127 72-106 70-106
47 27 25 45 34 36
10.0 8.6 7.9 9.0 9.2 9.2
1.95 1.40 1.40 1.35
0.52 0.24 0.24 0.23
8 9 24
79-1 18 81-122 73-118 72-120
39 41 45 48
0.7 0.7 0.4 0.9 0.7 0.2 0.1
2.35 2.35 2.00 2.45 2.35 2.60 2.65
0.73 0.73 0.57 0.75 0.73 0.76 0.77
8 11 17 21 24 25 88
75-120 82-126 77-120 79-122 81-126 77-118 75-122
45 44 43 43 45 41 47
694 1050 1240 1545
0.1 0.5 0.7 0.9
0.22 0.69 0.72 0.74
30 13 30 21
91-129 99-135 106- 29 86-133
688 696 895 978 1145 1245 1230 1195 1150
0.2 0.1 0.2 0.3 0.6 0.5 0.5 0.3 0.2
1.05 2.25 2.35 2.45 2.00 2.05 2.10 2.25 2.40 2.45 2.45 2.55 2.40
0.57 0.60 0.63 0.71 0.73 0.74 0.74 0.76 0.73
8 26 8 23 8 30 50 8 21
124122122126123127122124124-
51
850 840 890 870 695
0.2 0.2 0.2 0.2 0.2
1.90 1.90 1.90 1.90 1.90
0.46 0.46 0.46 0.46 0.46
13 16 12 12 13
0.1 0.1 0.1 0.1 0.1 0.1
1.25 0.85 1.65 1.25 1.05
988 984 983 984
0.5 0.4 0.4 0.3
1560 1130 1075 1550 1180 1195 1285
1 268
Evaluation Data
To establish the effectiveness of emulsification, a rapid and reasonably ac-
Summary of Essential Experimental and Calculated Data Total Energy/Lb. of -4sphalt, Watt-Hours AV. Asphalt Particle AV. Based upon Based upon Temp., O F. Wt ., Vol., current average Time, lld Min. Rise Lb. c u . /A Ratio rise current Range
0.22 0.19 0.30 0.22 0.21 0.21
695 695 798 700 694 692
sifier a t room temperature. Shaft speed was 700 r.p.m. and mixing time was 16 hours. The slurry was aged for at least 1 week before use. 2. The bentonite slurry was diluted to 570 concentration. mixed at 700 r.p.m.. and heated to the desired initial temperature. 3. The p H of the slurry was adjusted to neutrality with standard buffer, and the viscosity was increased from 200 to 700 centipoises by adding a constant amount of sulfuric acid. 4. The asphalt was heated to 260" F. and circulated for 15 minutes before emulsification. 5. The asphalt was then added to the unit at various rates and the bulk temperature, shaft speed, line current. and voltage recorded every 2 or 3 minutes in each run. 6. A homogeneous quart sample was retained from each 2.5-gallon batch of emulsion for quantitative data such as viscosity and particle size determination. Complete data are summarized in Table 1.
Total Surface Aiea o f dsphalt/Lb,. Asphalt, sq.M
697. 3333 592 4840 1495 4050
5.7 13.3 10.0 8.0 9.0 12.6
2.34 3.79 5.36 6.22 1.22 0.45
3.38 4.65 8.72 8.56 3.61 4.78
382 271 486 214 311 272
9.3 9.2 9.3 8.9
556 726 1317 863
5.73 6.04 2.66 2.30
10.10 7.57 6.82
430 377 356 384
8.6 9.3 9.2 8.9 8.9 9.2
2100 723 710 726 487 666 169
7.3 6.0 10.6 8.7 14.7 8.7 8.3 13.0 6.7 9.3 12.0
5.61 9.61 6.12 18.23 14.22 6.28 7.14
12.60 18.50 16.80 39.70 34.60 35.20 127.00
335 408 407 442 433 427 719
38 36 23 47
8.9 9.2 7.1 8.6
464 203 343 465
11.12 17.22 36.50 18.73
44
27 22 29 22 28 17 14 27 20
9.2 9.2 10.0 9.8 10.0 9.2 9.2 9.6 8.9
417 199 250 173 153 254 199 205 173
27.20 26.60 24.14 29.00 26.12 35.60 38.30 26.60 29.60
15.60 27.60 68.30 36.50 32.80 47.70 30.20 49.60 32.80 65.30 88.10 35.70 53.40
447 594 528 447 429 549 492 591 608 508 544 511 556
100- 33 75- 17 84- 19 82- 19 75- 13
33 42 35 37 38
9.8 9.6 8.9 9.6 9.6
48000 47000 40300 1790 240
79.80 70.00 79.80 72.90 69.80
86.20 78.30 86.20 79.40 76.70
99 97 109 254 593
17
lNDUSTRlAL AND ENGINEERING CHEMISTRY
44
51 48
51 44 36
51
7.1
7.0 7.7 9.4 7.0 5.4 5.4 5.2 5.7
5.5 5.7 5.7 4.3 5.0 8.0 7.3 9.0 8.7 9.0
5.51
ASPHALT EMULSIFICATION 1000
I Figure 3. Correlation of energy requirements with particle size
curate method of measuring the average particle volume was developed. The literature (2) did not give a method of the desired simplicity, although one particular treatise (3) ultimately led to the development of this described method. The average particle volume made possible a calculation of the surface area which may affect emulsion properties such as initial viscosity and viscosity stability, as well as dried film properties such as reemulsibility, weatherability, tensile strength, ductility, cohesion, and adhesion. The particle size distribution is also a factor influencing many of these properties. I n this method, a 5-gram sample of emulsion of known asphalt concentration is diluted to a convenient level; this usually approximates 1 gram of emulsion in 400 ml. of water. One drop of this diluted material is placed in the bloodcell counting chamber and the number of particles in a given volume determined a t 150 magnification. The determination is very simple. The amount of asphalt in the calibrated volume of the blood-cell chamber is known from emulsion concentration and dilution. The number of particles for dividing this amount of asphalt is determined by microscopic examination of the counting chamber. T h e total volume of asphalt divided by the number of particles gives the average particle volume, which is calculated from the formula indicated
200
400
I
600
800
Total &-face Area Developed Per Lb. Asphalt (sq. meters)
Figure 4. Correlation of energy requirements with surface area developed
p3 =
asphalt content X wt. (g.) emulsion 100 X in emulsion, % in final dilution average number of particles over counter unit area where p 3 = average particle volume in cubic microns The accuracy of the method varies with the particle size range as indicated below: Particle Volume Range, Cu. Microns
Standard Deviation, Cu. Microns
150- 250 250- 500 500-1000 1000-5000
30.6 39.8 80.7 417.0
I n the 150 to 250 cubic microns range the deviation was 30 cubic microns. I n the larger size range the deviation was 400 cubic microns. For comparison, a sphere with a diameter of 5 microns has a particle volume of 70 cubic microns. The average particle volume is a useful quantity in that it gives a single arithmetic number for comparing emulsions whose particles have different shapes.
Calculations
This average particle volume may be related to individual changes in shaft speeds and rates of addition, but in this
work only the relation of total energy input to the average particle volume was determined for each of the 30 controlled runs. Energy has been introduced in two forms. The heat energy supplied to the bentonite slurry expressed in watt-hours equals : Eaest = 4.5 ( t 70)
-
where t = initial temperature F. and 4.5 is a unit conversion factor for the batch size and specific heat of the slurry. Reference temperature was 70" F. O
T h e mechanical energy required for emulsification expressed in watt-hours equals : EMechenicai
=
.\/3 E I
COS
0t
where E = line voltage, volts Z = line current, amp. cos e = power factor (characteristic of the motor used under the given loading conditions) t = timeofrun, hours The developed surface area, expressed in square meters per pound of asphalt, equals: Area =
454 X weight emulsion, lb.
x D
weight asphalt, lb. X 1OI2
where VOL. 49, NO. 8
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1269
1000
-
800
m
,$
.B 600 0
u
B 00 400 Y
8 d g:
-4 200
0 Figure 5.
2
4 6 vol. Conc. H2SO4 (ml.) Apparent Viscosity (centipoises)
Acid treatment of 5% bentonite suspension
Figure 6. Correlation of initial suspension viscosity and asphalt particle size
A.
Mixed 2 hours at 100’ C. B. Mixed 16 hours at 75’ C. Sample size 400 ml. Viscosity determination by Brookfield viscometer
D
=
area per cu. cm. of emulsion as calculated from average particle volume
The results for the 30 runs have been plotted and equations calculated by the method of least squares (Figure 3). This log-log plot relates energy requirements per pound of asphalt to the resulting average particle volume in cubic microns. A calculation based upon this equation indicates that in this unit the power cost would be $3.60 per ton of asphalt to obtain an emulsion with an average particle volume of 150 microns. This calculation assumes an electrical energy cost of $0.06 per kilowatt hour. This semilog plot (Figure 4) relates energy requirements per pound of asphalt to the surface area in square meters developed per pound of asphalt.
have been used effectively in similar systems (70). This variation in sulfuric acid treatment also affects the average particle volume as indicated in this semilog plot. In Figure 6, average particle volume is plotted against sulfuric acid level. These data are for runs carried out at constant shaft speed, asphalt addition rate, and temperature. It is not clear whether the effect noted is strictly a viscosity effect, or is also related to slurry pH. However, the lack of asphalt breakdown a t the low acid levels indicates the importance of such treatment. The average particle size without acid treatment (48,000 cubic microns) indicates a particle diameter of about l I 8 inch, which is a very poor degree of dispersion. Conclusions
Effect of Acid Treatment
Several runs made a t different acid levels illustrate the effect of acid treatment of the bentonite slurry upon emulsification (Figure 5). The susceptibility of bentonite suspensions to relatively low concentrations of bases and neutral salts, as well as acids, is well known ( 7 ) . This graph relates slurry viscosity to acid concentration. The effect of temperature upon the degree of clay hydration, as indicated by apparent viscosity, is also noted. All controlled runs were made a t the 5-ml. sulfuric acid level shown here to be on the flat portions of these viscosity curves. The apparent viscosities were obtained with a Brookfield viscometer although other types
1 270
For the system described : 1. Acid treatment of the bentonite slurry is necessary for adequate dispersion or emulsification of the asphalt. 2. Emulsification is most satisfactory when the bentonite slurry temperature exceeds the softening or melting point of the asphalt. The fifth series of runs (summarized on the data sheet) in which the minimum mass temperature was 122’ F. resulted in consistently smaller average particle volumes. The average temperature was in each case above the specified softening point of the asphalt. The liquid dispersed with greater ease than the thermoplastic solid. 3. The average particle volume method developed provides a convenient
INDUSTRIAL AND ENGINEERING CHEMISTRY
means of determining effectiveness of emulsification, and may be useful in studying various emulsion properties. 4. The method of relating energy requirements to particle size or developed internal surface area may be useful in studying chemical treatments in other emulsification systems. Literature Cited
(1) Rergman, \V. E., Vt’oild 011 134, No. 5,1’0-8: No. 6, 122-33 (1952). ( 2 ) Dalle Vallk, J. M.., "MicrometriesThe Technology of Fine Particles,” Pitman Publ., New York, 1948. (3) Fullman, R. L., J. M e t & 5 , 447--52 (March 1953). (4) Hauser, E. A., IC Beau, D. S., in “Colloid Chemistry, Theoretical and Applied,” (J. Alexander, editor), vol. VI, chap. 7, Reinhold, S e w Tork, 1946. (5) Kirschbraun, L., Can. Patent 279,241 (Feb. 27,1927). ( 6 ) Kirschbraun, L., U. S. Patent 1,302,810(May 6, 1919). ( 7 ) Kirschbraun, L., %bid. reissue, 15,944 (SOT-. 11, 1924). (8) Kirschbraun, L., (to Flintkote C o . ) , dbid.,330,872 (Feb. 7, 1930). ( 9 ) Neppe, S. L., Petroleum Rejner 31, 137-42, (February 1952); 184--8 (-4pril 1.952). (10) Olphen, van H., Discussions Furuduy SOC. Yo. 11, 82-4 (1951). (11) Traxler, R. N., Romberg, J . W., 1.1.11.ENG.CHEW44, 155-8 (1952).
RECEIVED for review July 19, 1956 ACCEPTED January 2, 1957 Division of Industrial and Engineering Chemistry, 129th Meeting, ACS, Dallas, Tex., April 1956.
