SULFUR-ASPHALT DISPERSIONS ISAAC BENCOWITZ Texas Gulf Sulphur Company, Newgulf, Texas
Grinding is continued for 24 Sulfur ground with asphalt and kerosene hours. The pastes are then reamong the earliest and forms stable suspensions from which aquemoved and stored in glass most thoroughly studied bottles to be used as stock from ous emulsions can be prepared, using a sulcolloids. Numerous investiwhich emulsions are made, fonated alcohol as an emulsifying agent. gators since 1747 have sugA series of stock pastes conEmulsions containing as little as 1.5 per taining different proportions of gested various methods for the three constituents were prethe preparation of colloidal cent sulfur or as much as 70 per cent repared. In all cases the prosulfur (S). The best method 6 months, than mained stable for more portion of kerosene was someof preparing sulfur suspenwhat less than the minimum either standing on the shelf or with interdesired for emulsification. A sions a r e indirect chemical mittent shaking. The grinding, though few grams of the paste (5 to processes. Comparatively 25) are then weighed out into conducted in a specially constructed little is known about direct large test tubes (300-cc. caphysical methods of obtaining grinder, can be accomplished in any ball pacity), and variable quantities of kerosene are added. The aqueous suspensions from elemill and the emulsion is formed by hand suspensions thus formed are mental sulfur. stirring. Violent stirring is not required. emulsified by adding a 5 per I n 1910 von Veimarn sugcent aqueous solution of an The viscosities of these emulsions seem to gested mechanical grinding emulsifying agent (sodium oleyl be independent of the asphalt concentrasulfate). The solution is added with i n e r t substances as a in small steps, and the emulsion method of obtaining disperse tion, and are determined by a function exis stirred by hand between each systems. Senji Utzino, followpressed by the square of the kerosene conaddition, using a long glass rod. ing von Veimarn's suggestion, A t higher dilutions the stirrin centration divided by the product of the is done by shaking the stopperel obtained colloidal sulfur by sulfur and the water concentrations. glass tube. A mechanical stirprogressive grinding of sulfur rer may be used. But violent The usefulness of these emulsions as inwith glucose. N. Pihlblod stirring is very likely to result ground sulfur with urea. secticides and ovicides is suggested. only in partial emulsification. This is especially true at the However, sulfur suspensions higher dilutions. o b t a i n e d b v Dronressive Instead of adding the emulsifying agent as an aqueous grinding are "sometimes so polydisperse that a sediment solution, it can be added directly to the oil subpension in of coarse particles could be noticed soon after preparation" concentrated form. Attempts at reversing the order of ad(1). dition, such as adding the oily suspension to the water or A German patent describes a process of grinding sulfur with adding parts of each alternately failed to result in stable emulsions. Addition of the aqueous solution of the emulsifying glue; a French patent incorporates finely divided sulfur with agent under the surface of the oily suspension resulted in no a saccharate of a n alkaline earth (2). improvement. I n this paper a method is described for, and some of the MATERIALS USED. Crude sulfur was crushed to pass a 10-mesh properties are given of emulsions obtained by grinding sulfur sieve. The emulsifying agent was Modinal, a sodium oleyl sulwith asphalt and kerosene. The sulfur in these suspensions fate preparation. The asphalt was prepared from Texas and Mexican crude, steam- and air-blown' penetration was 35 at is polydisperse but i t does not settle out, and emulsions 25" C., 100 grams, 5 seconds; ring and ball softening point was thus prepared remained stable for more than 6 months. 75" C. The distillation range of the kerosene used was 182" C. initial and 285' final; viscosity was 395 seconds at 15" C.; specific gravity was 0.8. Method of Preparation
ULFUR hydrosols a r e
S
" .
-
An ordinary ball mill may be employed as a grinding mechanism. However, the emulsions described in this pa er were prepared in a specially designed grinding a paratus. ?t consists of two heavy rollers, 9 inches in diameter 723 cm.) and 2 inches (5 cm.) wide, revolving about a common horizontal and vertical axis. They revolve inside a deep pan 15 inches (38 cm.) in diameter, and as they revolve they crush the material while rolling over it. Several scrapers strategically mounted on the revolving member direct the material toward and under the advancing rollers. The grinder is char ed with 2 pounds (907 grams) of crude sulfur previously crushef to pass a 10-mesh sieve. The desired proportion of as halt and kerosene are then added. As much as 250 grams of aspgalt may be digested with 350 cc. of kerosene on a hot water bath to yield a fluid suspension. This suspension can then be added to the sulfur. But when larger proportions of asphalt are desired, the asphalt must be added separately in lumps. This makes grinding more difficult, inasmuch as it takes more time t o masticate the lumps of asphalt than to grind the sulfur. Sulfur can be ground more finely in the presence of asphalt and kerosene than it is possible to do in the presence of either alone or in the absence of both.
Emulsification For any given sulfur-asphalt ratio there is a minimum percentage of kerosene below which emulsification will not take place, and the higher the asphalt content, the higher the minimum kerosene requirements. On the other hand, when the proportion of kerosene for any given sulfur-asphalt ratio exceeds a certain value, the suspension formed, though emulsifiable, will separate in two layers on standing. Between these two limits of kerosene concentrations, uniform emulsifiable suspensions are formed. Table I gives these limited kerosene values for the indicated sulfur-asphalt ratios. The results are plotted in Figure 1. The shaded area represents concentrations of uniform suspensions which are emulsifiable. T o the right of this area the suspensions are emulsifiable but not uniform; two layers are formed on standing. To the left of this area the suspensions are uniform but not emulsifiable. 1165
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VOl. 33, No. 9
The maximum amount of asphalt which can be incorporated with sulfur under the described conditions is that which yields a sulfur-asphalt ratio of 0.6.
with water the change in concentration will follow line BEO, and stable emulsions will result until the line intersects the experimental curw at E. Dilution beyond this point results in a water phase and the emulsion will break. If the concentration of the original suspension is represented b y a point such as D below point C, the change in concentration due to TABLEI. MINIMUMAND MAXIMUMKEROSENECONCERTRA- the addition of water will follow line DGFO. At first an emulTIONS AND CORRESPONDING SULFUR-ASPHBLT RATIOS O F EMULSIsion in equilibrium with a separated layer of kerosene is FIABLE SUSPENSIONS formed. However, as more and more water is added, the Sulfur/asphalt, weight 20.010.1 G.0 3.6 2.7 0 . 8 0 . 6 volume of the emulsion increases and the volume of keroKerosene, grarna/lpO grams suspension sene decreases. When point G is reached and beyond, uniMinimum 15.0 1 6 . 5 17.0 17.5 1 8 . 2 2 6 . 0 31.0 Maximum 18.0 2 2 . 0 30.0 36.0 3 7 . 0 3 8 . 7 39.5 form emulsions result. At point F and beyond, excess water appears and the emulsion is unstable. Pastes of different sulfur-asphalt ratios will yield similar emulsification diagrams. But the positions of the shaded areas and their shape will change. Figure 3 shows two concentration fields of stable emulsions made from two pastes. The sulfur-asphalt ratio of one is 0.6, the lowest ratio yielding satisfactory emulsions. The sulfur-asphalt ratio of the other is 10.1, which is not the highest sulfur-asphalt ratio yielding stable emulsions; the highest is 32. But the liminal boundaries of emulsions made from pastes with sulfur-asphalt ratios
f0
I 20
30
40
J
50
Kerosene, per cenf by We/ghf
FIGURE1. FIELDOF STABLESULFUR-ASPHALT-KEROSENB SUSPENSIOKS EMULSIFIABLE IN AN AQUEOUS SOLUTIOK OF AN EMULSIFYING AGENT
A paste of any one sulfur-asphalt ratio diluted with kerosene and then emulsified with a 5 per cent solution of the emulsifying agent will form several different emulsions. Figure 2 shows an emulsification diagram of a paste whose sulfurasphalt ratio is 6.08. Only kerosene and water are added to the paste, so that throughout the series of dilutions the original sulfur-asphalt ratio is not changed. If from this paste kerosene were removed, the change in concentration mould follow straight line ABD upward from point A . Experimentally, however, kerosene is added, and the concentration changes follow straight line ABD downward from point A. Concentrations between points A and C yield uniform stable suspensions. When the addition of kerosene is continued below point C, a kerosene phase appears on standing. However, any suspension along line ABD and below A is emulsifiable, whereas mixtures above point A are not. When an aqueous solution of the emulsifying agent is added to any of the emulsifiable suspensions, the concentration changes follow straight lines joining the given point on line ABD with the origin. If the oil suspension is represented by point E within the limits of A and C, then on emulsification
2. PHASE DIAGRAM OF SULFUR-ASPHALTKEROSENE-WATER EMULSION WITH A SULFURASPHALTRATIO OF 6.08 FIQURE
higher than 10.1 do not shift sufficiently to show a marked difference on the triangular diagram. The data plotted in Figure 3 are given in Table 11. The concentrations of kerosene and water, in grams per 100 grams of emulsion, are plotted against the combined concentrations of sulfur and asphalt. Thus, the three variables add up to 100. The concentration
September, 1941
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settling for more than 2 months. The emulsions were made by adding the same volume of a 5 per cent solution of the emulsifying agent and kerosene to 15 grams of the different pastes. These emulsions contain, per 100 cc., 84.5 cc. of a 5 per cent solution of emulsifying agent, 11 cc. of kerosene, and 7 grams of the combined weight of sulfur and asphalt. Obviously, therefore, the actual amount of sulfur and asphalt as well as the sulfur-asphalt ratio varied in the eleven different emulsions of Figure 4. However, the sulfur content of the emulsions of sulfurasphalt ratios between 10.1 and 32 varied from 6.45 to 6.78, respectively, while the sulfur content of emulsions of sulfur-asphalt ratios between 10.1 and 7.6 varied from 6.45 to 6.35, respectively. It seems justifiable, therefore, to assume that the ratio of sulfurasphalt rather than any other factor determines the stability of the emulsion.
Viscosity The viscosities of these emulsions were determined in a modified Stormer viscometer. The cylindrical rotor had been replaced by a prong-type rotor. The temperature was ,%/fur p/us Asphdf, par cen f by Weighf maintained a t 30' =t0.5" C. by a stream of running water from a large thermostat. FIGURE 3. SULFUR-ASPHALT-OI~WATER EMULSIONB Emulsions a t the lowest dilutions, especially those with low kerosene content, are very thick creamlike pastes. They exhibit pronounced thixotropic properties. When the rate of field of emulsions made of pastes with sulfur-asphalt ratios shear in seconds per 100 revolutions is plotted against the between 0.6 and 10.1 will be included within the liminal stress in grams, a curved line results (Figure 5). Such curves boundaries of Figure 3. obtained with a series of rising stresses do not coincide with Not every sulfur-asphalt ratio yields emulsions of equal similar curves obtained with decreasing stresses. I n other stability. Figure 4 shows eleven emulsions as they appeared
FIOURE 4. R,ELATIVEI STABILI 'TIES OF
%
after 8 months of standing on the shelf. The corresponding sulfur-asphalt ratios are marked on the tubes. The most stable emulsion is formed from a paste of a sulfur-asphalt ratio of 10.1. Yet all these emulsions showed no signs of
EnamJSIONS DETERMINED BY THE soILFTJR- ASPHALTRATIO
words, hysteresis is indicated. The term "viscosity" applied to these emulsions is obviously inaccurate. To obtain a series of figures even for relative comparison, it was necessary to establish two curves for each emulsion-one with dif-
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TABLE11.
RANGEO F EMULSIONS O F EXTREME SULFUR-ASPHALT RATIOS
COMPOSITION
-Water BoundarySulfur Asphalt Kerosene Water
--Kerosene BoundarySulfur Asphalt Kerosene Water
VOl. 33, No. 9
ferent rising stresses and one with decreasing stresses. The average stress for a given rate of shear (grams to cause 100 revolutions in 20 seconds) warj read from these two curves.
Sulfur-Asphalt Ratio 0 6 28.2 27.9 27.1 26.1 25.2 23.6 17.7 17.4 14.8 10.3 10.2 9.7 8.2 6.6 5.9 4.3 3.4 2.6 1.9
46.7 46.8 44.8 43.3 41.8 39.2 29.0 28.6 24.3 17.0 16.6 16.0 13.5 10.9 9.7 7.0 5.6 4.3 3.1
3 2 4 6 6 0 8 7 11 2 15 8 28 0 27 5 35 1 50 9 53 4 54 1 60 7
21.9 207 221 21.9 21 8 21 4 25 3 26 5 25 S 23 8 19 8 20 2 17 6 15 8 14.1 12.5 9 3 7 3 5 0
66 7
70.3 76 2 817 858
23.9 23.4 23.1 21.6 17.0 14 9 14.0 10.3 8.3 7.3 6.3 5.4 4 1 4 0 3.5 1.2
39.1 38 3 37.9 36.4 27.9
24 7 23 0 16 9 13.6 11 9 10 4 9 0 6 8 6 6 5.7 2 8
37 38 39 37 32
0
3 0 3 8 .32 Y
.A3 4 26 b 23 1 24 9 20 1 18 6 176 15 4 16 3 10 0
5 7
22 3 27 5
29.6 46 2 55.0 55 9
b3.2 G7 0 715 z4.0 14 5 S6 0
900
Sulfur-Asphalt Ratio 10 1 76.0 72.8 71.2 70.3 69.1 67.6 64.9 61.4 59.7 56.5 54.0 61.8 43.7 34.5 27.1 22.3 17.4 16.4 14.4 13.1 12.1 10.9 9.9 8.4
7.6 7.2 7.1 6.9 6.8 6.7 6.3 6.2 5.9 5.8 5.3 5.3 4.3 3.4 2.7
2.2
1.7
1.5 1.3 1.3 1.2 1.1 1.0 0.8
142
138 126 139 140 14 0 13 7 15.7 12.4 14 6 13 2 14 6 11 2 9 3 97 20 6 7 4 8 6 8
3 2 6 2 9 1 8 9 9 1 11 7 15 1 16.7
22.0
23.1 27 5 28 3 40 8 528 61 80 5 742 783 775
:; :;: 4 7
5 1 6 1
zi; 542
42 7 380 34s 296 292 241 234 225 14 1 134
7 5 5 4 3 3
5 0 3 2
8 5
2 9
2 2 2 2 1
210 2d4 25d 23 0 204 225 173
9 9 3 2 4
187 182
8 9
1 3 o 9
6 2 5 9 5 6
o 6 0 6 o 5
10 8
1 4 8 194 1.3 5
113 10 5
6
122 12 2
833 84.0 857
0 0
156
I52 do 1 376 392 502
494
FIGURE 6. SPRAYIYG Go.Lr
TITH
SCLFUREMIJLSIO~
348
595 562 71 0 710 79.7
::
82 4 813 81 3
:i ’8
When the average stresses are plotted against the function K 2 / S X W , a characteristic curve is obtained. I
