Bimodal emulsion and its method of preparation

A stable, low viscosity bimodal oil in water emulsion having an emulsifier, a continuous water phase and a discontinuous oil phase having an oil:water ratio of from about 70:30 to about 85:15 by weight, the discontinuous oil phase being characterized by two distinct oil droplet sizes D.sub.L and D.sub.S wherein D.sub.L is about 10 to 40 microns and D.sub.S is less than or equal to 5 microns, the ratio of D.sub.L /D.sub.S is greater than or equal to 4 and about 45 to 85% by weight of the oil is in oil droplet size D.sub.L.

BACKGROUND OF THE INVENTION 
The present invention relates to a stable, low viscosity bimodal oil in 
water emulsion and, more particularly, a bimodal oil in water emulsion 
having a discontinuous oil phase characterized by two distinct mean 
diameter oil droplet sizes. The present invention further relates to a 
method for producing a stable, low viscosity bimodal oil in water emulsion 
whose viscosity does not age over time. 
Reserves of viscous hydrocarbons are plentiful. Low API gravity, viscous 
hydrocarbons found in Venezuela, Canada, the Soviet Union and the United 
States have viscosities ranging from 10,000 to more than 500,000 
centipoise at ambient temperatures and API gravities of less than 15. 
These oil reserves are generally located at remote places far away from 
the large oil consumption centers of the world. 
Viscous hydrocarbons of the type aforesaid are currently produced either by 
steam injection in combination with mechanical pumping, mechanical pumping 
itself, or by mining techniques. Because of the high viscosity of the 
viscous hydrocarbons it is impossible to handle them by conventional 
equipment. The alternative methods developed for handling viscous 
hydrocarbons tend to be very expensive. 
The formation of emulsions of viscous hydrocarbons in water allows for 
improved handling of the viscous hydrocarbons as, under certain 
conditions, the viscous oil in water emulsions have lower viscosities than 
the viscous hydrocarbons themselves. It is well known in the art to 
transport viscous hydrocarbons by first forming a viscous hydrocarbon in 
water emulsion and thereafter pumping the emulsion which is at a lower 
viscosity through conventional pipelines. Generally, the viscous 
hydrocarbon in water emulsions formed for transportation in the manner 
described above comprise emulsions where the dispersed phase content of 
viscous oil in the oil in water emulsion is less than or equal to 70% by 
weight. The oil content is classically limited to a maximum value of 70% 
by weight as a result of the fact that emulsion viscosity increases in an 
exponential factor when the dispersed oil phase increases beyond 70% by 
weight. In addition, for viscous hydrocarbon in water emulsions having 
dispersed oil phase concentrations of greater than 70% by weight and 
monomodal mean diameter droplet size distribution, conventional means for 
transporting the emulsions become inoperative due to the high viscosity of 
the emulsions and the complexity of the realogical behavior of the 
emulsions as a result of the visco-elastic nature of these emulsions. It 
is well known in the prior art that the realogy properties of oil in water 
emulsions are significantly influenced by distribution and the mean 
diameter oil droplet size. Thus, for any known viscous hydrocarbon in 
water ratio in an oil in water emulsion and for any given mean diameter 
oil droplet size distribution, the viscosity of the resultant oil in water 
emulsion diminishes when the oil droplet size distribution becomes more 
poly-dispersed. In other words, a mono-dispersed emulsion has a viscosity 
greater than the same emulsion with a poly-dispersed droplet size 
distribution. 
It is highly desirable when transporting these high dispersed phase 
concentrated viscous hydrocarbon in water emulsions by pipeline or tanker 
over large distances to increase the internally dispersed viscous 
hydrocarbon phase to a maximum possible value. By maximizing the viscous 
hydrocarbon content of the emulsion the cost for transportation is 
decreased per unit of viscous hydrocarbon. Furthermore, when these viscous 
hydrocarbon in water emulsions are used directly as fuels in power plants, 
the greater viscous hydrocarbon concentration in the emulsion results in a 
corresponding greater energy output by unit volume of the emulsion. 
Accordingly, it is the principal object of the present invention to provide 
a viscous hydrocarbon in water emulsion characterized by a high internal 
phase concentration of viscous hydrocarbon, a relatively low viscosity and 
stable viscosity over time. 
It is a further objection of the present invention to provide a viscous 
hydrocarbon in water emulsion as aforesaid which is characterized by a 
distinct bimodal dispersed viscous hydrocarbon oil phase. 
It is a still further object of the present invention to provide a viscous 
hydrocarbon in water emulsion as aforesaid wherein the viscosity of the 
emulsion can be readily adjusted and modified without further shearing of 
the emulsion product. 
It is a further principal object of the present invention to provide a 
method for preparing a stable, low viscosity bimodal viscous hydrocarbon 
in water emulsion which is resistant to aging over time and may have 
viscosity modifications made to any desired value for fulfillment of any 
end use requirement. 
SUMMARY OF THE INVENTION 
The foregoing objects and advantages are achieved by way of the present 
invention which provides for a stable, low viscosity bimodal viscous 
hydrocarbon in water emulsion and a method for making same. 
In accordance with the present invention the stable, low viscosity bimodal 
viscous hydrocarbon in water emulsion of the present invention comprises a 
continuous water phase and a discontinuous oil phase wherein the 
hydrocarbon to water ratio of from about 70:30 to about 85:15 by weight. 
In accordance with a critical feature of the emulsion of the present 
invention, the discontinuous viscous hydrocarbon oil phase is 
characterized by two distinct oil phases having mean diameter oil droplet 
sizes of D.sub.L and D.sub.S respectively wherein D.sub.L is about 15 to 
30 microns and D.sub.S is less than or equal to 5 microns. In accordance 
with the preferred embodiment of the present invention, the mean diameter 
oil droplet size D.sub.S is less than or equal to 3 microns. The 
hydrocarbon in water emulsion of the present invention is further 
characterized in that the ratio of D.sub.L /D.sub.S is greater than or 
equal to 5 and preferably greater than or equal to 10 and about 45 to 85% 
by weight, preferably 70 to 80% by weight, of the viscous hydrocarbon is 
of mean diameter oil droplet size D.sub.L. In accordance with a further 
preferred feature of the present invention, the stable, low viscosity 
bimodal viscous hydrocarbon in water emulsion exhibits superior aging 
properties over time when the maximum salt content of the hydrocarbon in 
water emulsion is maintained at below 30 ppm. 
The method for preparing a stable, low viscosity bimodal viscous 
hydrocarbon in water emulsion as set forth above comprises providing a 
dehydrated viscous hydrocarbon feedstock with a salt content of less than 
15 ppm and thereafter preparing two separate viscous hydrocarbon in water 
emulsions wherein one of the viscous hydrocarbon in water emulsions has a 
dispersed viscous hydrocarbon phase having a mean diameter droplet size of 
less than 5 microns and the other viscous hydrocarbon in water emulsion 
has a dispersed phase of viscous hydrocarbon having a mean oil droplet 
size of from between 10 to 40 microns, preferably between 15 to 30 microns 
wherein the ratio of viscous hydrocarbon to water in the emulsions is from 
about 70:30 to about 85:15% by weight. Thereafter, the two distinct 
viscous hydrocarbon in water emulsions are mixed together in a proportion 
so as to obtain about 45 to 85% by weight, preferably 70-80% by weight, of 
the oil in the mean oil droplet size of between 10 to 40 microns, 
preferably between 15 to 30 microns thereby forming a final hydrocarbon in 
water emulsion having a viscosity of less than 1500 cps at 1 sec.sup.-1 
and 30.degree. C. wherein the viscous hydrocarbon material phase exists as 
two distinct, definable mean diameter droplet size distributions. 
The method of the present invention results in a stable, low viscosity 
bimodal viscous hydrocarbon in water emulsion which is characterized by a 
high internal oil phase concentration, a relatively low viscosity and a 
stable viscosity over time. The viscous hydrocarbon in water emulsion 
product of the present invention is readily transportable by conventional 
equipment, either pipeline and/or tanker, and exhibits excellent aging 
properties. The method of the present invention allows for adjusting the 
viscosity of the viscous hydrocarbon in water emulsion without subjecting 
the emulsion to further shearing action. 
Further objects and advantages of the present invention will become 
apparent hereinbelow. 
DETAILED DESCRIPTION 
The present invention is drawn to a stable, low viscosity bimodal viscous 
hydrocarbon in water emulsion which is characterized by low viscosity and 
superior aging properties. The present invention is further drawn to a 
method for the preparation of such a bimodal viscous hydrocarbon in water 
emulsion. 
When handling viscous hydrocarbons, particularly heavy and extra heavy 
viscous crude oils, natural bitumens or refinery residuals, a viscous 
hydrocarbon in water emulsion having minimal viscosity values can be 
produced by preparing an emulsion having two distinct dispersed oil phases 
wherein each of the oil phases has a well defined mean diameter oil 
droplet particle size and where each size exists in a specific ratio 
relative to each other. It has been found that in order to obtain a 
stable, low viscosity bimodal hydrocarbon in water emulsion wherein the 
discontinuous oil phase within the continuous water phase has an oil to 
water ratio of about 70:30 to about 80:15% by weight, the discontinuous 
oil phase should be present in two distinct and definable oil droplet 
sizes, one having a large mean diameter droplet size (D.sub.L) and one 
having a small mean diameter droplet size (D.sub.S). In accordance with 
the present invention the small mean diameter oil droplet size 
distribution (D.sub.S) is less than or equal to 5 microns and preferably 
less than or equal to 3 microns and the large mean diameter oil droplet 
size distribution (D.sub.L) is about between 10 to 40 microns and 
preferably 15 to 30 microns. In order to obtain very low viscosities in 
the final hydrocarbon in water emulsion product it has been found that the 
ratio of the large size diameter oil droplet particles, D.sub.L, to the 
smaller diameter oil droplet particles, D.sub.S, be greater than or equal 
to 5 and preferably greater than or equal to 10. In addition, in order to 
achieve the lowest possible viscosity in the resultant hydrocarbon in 
water emulsion, 45 to 85% by weight and preferably 70 to 80% by weight of 
the viscous hydrocarbon in the hydrocarbon in water emulsion should be of 
oil droplet size D.sub.L, that is, 15 to 30 microns. In order to form a 
hydrocarbon in water emulsion which is resistant to aging, that is where 
the viscosity of the emulsion does not increase over time, the maximum 
salt content of the emulsion product should be preferably less than or 
equal to 5 ppm. 
The stable hydrocarbon in water emulsion product of the present invention 
is prepared by producing two distinct viscous hydrocarbon in water 
emulsion products having the preferred oil droplet sizes D.sub.L /D.sub.S 
described above and thereafter mixing the emulsions in preferred amounts 
so as to obtain the final product having the required weight percent oil 
in large droplet size D.sub.L. The oil to water ratio of each of the 
prepared hydrocarbon in water emulsions should range from about 70:30 to 
about 85:15. The emulsions are prepared using an HIPR technique described 
in U.S. Pat. No. 4,934,398. The hydrocarbons employed in the method of the 
present invention are viscous hydrocarbons characterized by API gravities 
of less than 15 and viscosities as great as 100,000 centipoise at 
30.degree. C. or greater. The resultant viscous hydrocarbon in water 
emulsion product is characterized by a viscosity of no greater than 1500 
centipoise at 30.degree. C. 
In order to insure proper aging properties of the resultant hydrocarbon in 
water emulsion product, the viscous hydrocarbon employed in forming the 
emulsions of the present invention should be dehydrated and desalted to a 
salt content of less than 40 ppm preferably less than 15 ppm. By 
controlling the salt content of the final emulsion product stability of 
the emulsion and superior aging properties of the emulsion are obtainable. 
The present invention allows for tailoring of the viscosity of resulting 
emulsions by controlling the amount of oil in the emulsion in the form of 
either distinct oil droplet size D.sub.L and D.sub.S. The viscosity 
modification can be changed therefor without modifying the hydrocarbon to 
water ratio and without sacrificing emulsion stability as a result of 
shearing and stressing energies normally required to change emulsion 
viscosity. In order to modify the viscosity of the bimodal emulsion of the 
present invention one need only to vary the proportion of large droplet 
sizes D.sub.L to small droplet sizes D.sub.S of the dispersed viscous 
hydrocarbon phase.

Further details and advantages of the product and process of the present 
invention will appear from the following illustrative examples. 
EXAMPLE 1 
Emulsions were prepared using HIPR technique as shown in U.S. Pat. No. 
4,934,398 using Cerro Negro natural bitumen from a Venezuelan Oil Field 
named CERRO NEGRO. The emulsions were made as shown in Table I using an 
aqueous solution of a surfactant based on a formulation named 
INTAN-100.RTM., a registered trademark of INTEVEP, S.A. and which is an 
alkyl-phenol ethoxylated emulsifier. The initial oil to water ratio was 
93/7, 90/10, 85/15, 80/20 by weight. The mixture was heated to 60.degree. 
C. and stirred changing the mixing speed and mixing time such as to obtain 
average droplet size distribution of 2, 4, 4, 20, and 30 microns and 
monomodal droplet size distribution. Once prepared such emulsions with the 
droplet size desired were diluted with water as to obtain a ratio of oil 
to water of 70/30, 75/25, 80/20 by weight. 
All emulsions were stabilized with 3000 mg/l of INTAN-100.RTM. with respect 
to the oil, except those with droplet size were of less than 3 microns 
which required about 5000 mg/l of INTAN-100.RTM. emulsifier. 
Emulsion properties are shown in Table I. 
TABLE I 
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BITUMEN/ DROPLET VISCOSITY 
WATER DIAMETER AT SEC.sup.-1 
EMULSION (by weight) 
MICRONS AND 30.degree. C. 
______________________________________ 
1 70/30 2.1 16.000 
2 70/30 4.3 11.000 
3 70/30 20.7 3.000 
4 70/30 29.8 2.500 
5 75/25 2.1 52.000 
6 75/25 4.3 30.000 
7 75/25 20.7 9.500 
8 75/25 29.8 6.000 
9 80/20 2.1 100.000 
10 80/20 4.3 38.000 
11 80/20 20.7 17.000 
12 80/20 29.8 8.500 
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Emulsions 2 and 3, those having oil:water ratio 70:30 and average droplet 
size distribution of 4.3 and 20.7 microns, were mixed together in 
different proportions and the viscosities of the resultant bimodal 
emulsions were measured. The results are shown in Table II below. 
TABLE II 
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% BY WEIGHT % BY WEIGHT 
EMULSION W/MEAN 
EMULSION W/MEAN 
VISCOSITY 
DROPLET SIZE OF 
DROPLET SIZE OF 
AT SEC.sup.-1 
EMULSION 
4.3 MICRONS 20.7 MICRONS 
AND 30.degree. C. 
__________________________________________________________________________ 
A 100 0 11.000 
B 75 25 5.000 
C 50 50 400 
D 25 75 90 
E 0 100 3.000 
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Table II shows that a relationship exists between the fraction of the oil 
phase of the emulsion in large droplet size distribution (20.7 microns) 
and small droplet size distribution (4.3 microns). In order to accomplish 
the lowest viscosity value both droplet fraction must be clearly defined 
as two identifiable and distinct size distributions. The relationship 
between the ratio by weight of the large droplet size diameter and small 
droplet size diameter for which the lowest bimodal emulsion viscosity is 
found about 25% by weight of small size droplets and 75% by weight of 
large size droplets. 
EXAMPLE 2 
Bimodal emulsions containing 75% by weight of a large droplet size emulsion 
D.sub.L and 25% by weight of a small droplet size emulsion D.sub.S in a 
total oil to water ratio in the final emulsion product of 70:30 were made 
from the emulsions of Table I as described in Table III below. 
TABLE III 
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RATIO BY VISCOSITY 
MEAN DROPLET 
MEAN DROPLET 
RATIO OF 
WT. OF OIL AT/SEC.sup.-1 
EMULSION 
D.sub.S MICRONS 
D.sub.L MICRONS 
D.sub.L /D.sub.S 
EMUL. D.sub.L /EMUL. D.sub.S 
AND 30.degree. C. 
__________________________________________________________________________ 
F 2.1 29.8 14 75/25 66 
G 4.4 29.8 7 75/25 90 
H 5.2 29.6 6 75/25 148 
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Table III shows the relationship between viscosity of a bimodal emulsion 
and the effect of the ratio of large mean droplet size to small mean 
droplet size (D.sub.L /D.sub.S) for emulsions with a ratio of oil:water of 
70:30% by weight. It can be seen, that the bimodal emulsion viscosity 
increases when there is an increase in the fraction of small mean diameter 
droplet size. However, all the viscosity values reported for emulsions F, 
G and H are far below the monomodal emulsions having 70% by weight oil as 
the dispersed phase. (See Table I) 
EXAMPLE 3 
With the emulsions as prepared in Example 1 which characteristics are shown 
in Table I, bimodal emulsions containing 75% by weight of a large droplet 
size emulsion D.sub.L and 25% by weight of a small droplet size emulsion 
D.sub.S in a total oil to water ratio in the final emulsion product of 
75:25 were produced as shown in Table IV. 
TABLE IV 
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MEAN DROPLET 
MEAN DROPLET RATIO BY WT. OF 
VISCOSITY AT/ 
EMULSION 
D.sub.S MICRONS 
D.sub.L MICRONS 
D.sub.L /D.sub.S 
EMUL.D.sub.L /EMUL.D.sub.S 
SEC.sup.-1 AND 30.degree. 
__________________________________________________________________________ 
C. 
I 2.1 20.7 10 75/25 180 
J 4.3 20.7 5.7 75/25 600 
K 2.1 29.8 14 75/25 150 
L 4.3 29.8 4 75/25 300 
__________________________________________________________________________ 
Table IV shows the relationship between viscosity and the ratio of large 
mean droplet size to small mean droplet size (D.sub.L /D.sub.S) for 
bimodal emulsions with an oil to water ratio of 75:25 by weight. 
It can be seen that a viscosity below 1500 cps at/sec.sup.-1 and 30.degree. 
C. can be obtained when the ratio of large mean droplet size to small mean 
droplet size (D.sub.L /D.sub.S) should be greater than or equal to 5. 
EXAMPLE 4 
With emulsions as prepared in Example 1 whose characteristics are shown in 
Table I further bimodal emulsions having different ratios of (D.sub.L 
/D.sub.S) and containing 75% by weight of a large droplet size emulsion 
D.sub.L and 25% by weight of a small droplet size emulsion D.sub.S in a 
total oil to water ratio in the final emulsion product of 80:20 were 
prepared as shown in Table V wherein the oil:water ratio of the emulsion 
was 80:20. 
TABLE V 
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MEAN DROPLET 
MEAN DROPLET RATIO BY WT. OF 
VISCOSITY AT/ 
EMULSION 
D.sub.S MICRONS 
D.sub.L MICRONS 
D.sub.L /D.sub.S 
EMUL.D.sub.L /EMUL.D.sub.S 
SEC.sup.-1 AND 30.degree. 
__________________________________________________________________________ 
C. 
M 2.1 20.7 10 75/25 1.100 
N 4.3 20.7 5.7 75/25 14.000 
O 2.1 29.9 14 75/25 450 
P 4.3 29.8 4 75/25 7.500 
__________________________________________________________________________ 
Table V shows the relationship between viscosity and the ratio of large 
mean droplet size to small mean droplet size (D.sub.L /D.sub.S) for 
bimodal emulsions with an oil:water ratio of 80:20% by weight. It can be 
seen that a bimodal emulsion having a ratio of oil:water of 80:20, in 
other words 80% dispersed oil phase, it is necessary that the ratio of 
large mean droplet size to small mean droplet size (D.sub.L /D.sub.S) 
should be greater than or equal to 10 in order to obtain a desired low 
viscosity below 1500 cps at 1 sec.sup.-1 and 30.degree. C. EXAMPLE 5 
With the emulsions prepared in Example 1 whose characteristics are shown in 
Table I, further bimodal emulsions were prepared having the different 
ratios of large mean droplet size emulsion D.sub.L over small mean droplet 
size emulsion D.sub.S by weight as shown in Table VI. 
TABLE VI 
__________________________________________________________________________ 
MEAN DROPLET 
MEAN DROPLET 
RATIO BY WT. OF 
VISCOSITY AT/ 
EMULSION 
D.sub.S MICRONS 
D.sub.L MICRONS 
EMUL.D.sub.L /EMUL.D.sub.S 
SEC.sup.-1 AND 30.degree. C. 
__________________________________________________________________________ 
Q 2.1 29.8 80/20 600 
R 2.1 29.8 75/25 450 
S 2.1 29.8 70/30 800 
T 2.1 29.8 65/35 1.500 
__________________________________________________________________________ 
Table VI shows the relationship between viscosity and proportion by weight 
of small mean droplet size to large mean droplet size (D.sub.L /D.sub.S) 
for bimodal emulsions with an oil to water ratio of 80:20 by weight. It 
can be seen that the viscosity of a bimodal emulsion having a ratio of 
oil:water 80:20, in other words 80 percent dispersed oil phase in 20% 
continuous oil phase can be modified by just changing the proportion of 
oil by weight in the small mean droplet and large mean droplet sizes. When 
there is an increase value in the portion of small mean droplets the 
viscosity decreases and then increases. 
This invention may be embodied in other forms or carried out in other ways 
without departing from the spirit or essential characteristics thereof. 
The present embodiment is therefore to be considered as in all respects 
illustrative and not restrictive, the scope of the invention being 
indicated by the appended claims, and all changes which come within the 
meaning and range of equivalency are intended to be embraced therein.