System for Producing Emulsions

1. Field of the Invention

This invention relates to the preparation of emulsions and more particularly it relates to apparatus for the continuous preparation of high internal phase ratio emulsions.

2. Description of the Prior Art

Various apparatus have been known and employed for the preparation of emulsions, and in the majority of applications, the apparatus was adapted to the preparation of emulsions only in batch unit processing. Some apparatus was proposed for the continuous preparation of emulsions. In such apparatus, the proportioning of the internal and external phases required precise metering devices, such as positive displacement metering pumps, and sophisticated controls to insure that these pumps delivered the proper ratio of internal and external phases. Then, the two precisely metered internal and external phases were passed to some type of a premixing device which produced a loose dispersion of the internal phase within the external phase. Then, a suitable pump was employed to force the loose dispersion through a mixer which provided the necessary shear for reducing the particle sizes of the internal phase within a continuous external phase, so that the dispersed phase was in droplet sizes of less than a few dozen microns so that a stable emulsion was produced. The mixing device employed elements which could be energized in a fashion that fluids passed between them were commuted to a finally divided state. The mixers can be generally classified as devices capable of producing high shearing, such as high speed impellers, colloidal mills, ultrasonic dispersers, and like machines where the internal phase was subject to high shearing action to be dispersed within the external phase.

Emulsions could be made continuously in such equipment but none of these known apparatus for producing emulsions can produce an emulsion with an internal-external phase ratio in excess of 75 to 25 percent by volume. First, the properties of these high internal phase ratio emulsions include non-Newtonian flow properties, thixotropic characteristics, and a high sensitivity to shear magnitudes which, if they exceed the stability point of the desired emulsion, cause an inversion between the internal and external phases. For example, emulsions containing 10 to 30% by volume internal phase can be made easily on a continuous or semi-continuous basis. However, as the amount of internal phase begins to rise above the 75% level, the unusual properties of the high internal phase ratio emulsions prevent the ready application of known apparatus for their preparation. One unusual property is the reduction of the effective viscosity of emulsified composition to approximately that of the external phase upon the application of shear. As this condition is approached, the viscosity of the emulsion composition changes rapidly, and this result rapidly changes the flow of the ingredient internal and external phase materials through the various metering and pumping devices. The pumping means may suddenly encounter a change of fluid condition from a relatively low viscosity to a very high viscosity and then suddenly to a reduced viscosity as the desired high internal phase ratio emulsion is obtained. This viscosity changing effect is not the actual viscosity as would be taken in a Fann viscosity meter, but rather is the apparent effective viscosity of the emulsified mass within the system. Reference may be taken to U.S. Pat. No. 3,565,817, where there is a detailed description of the composition preparation and properties of high internal phase ratio emulsions wherein the internal phase is present in excess of 75% by volume of the resultant emulsion. The description of this patent is incorporated herein, along with the additional references listed therein which describe the ingredients and desired emulsions having internal and external phase ratios above 75 to 25 percent by volume.

the problems with the great complexity of equipment for producing on a continuous basis the high internal phase ratio emulsions were avoided in a novel "System for Producing Emulsions", which is the subject of our pending application, Ser. No. 459,760, filed Apr. 10, 1974, now U.S. Pat. No. 3,946,994. This system provides for producing continuously at a selected rate, a stable highly viscous emulsion with an internal phase content above about 75% by volume within an immiscible external phase. In preparing some types of these high internal phase emulsions, field conditions causing temporary phase supply interruption, intermittent system operation and other operating causes, interfered with maintaining high quality emulsions. Also, the system had to be carefully started in production of the emulsion under these conditions. It is believed that these problems resided in some portion of the piping being filled with one phase not comingled with the other phase immediately before the pumping means.

The present invention provides a mixing means for distribution stepwise of the internal phase progressively in amount into the inverter phase immediately before the pumping means forming the desired emulsion. Sudden temporary upsets in phase supplies cannot produce instant flow of only one phase into the pumping means.

High internal phase ratio emulsions possess peculiar rheological properties. When subjected to sufficiently low rates of shear, they behave like elastic solids. As the rate of shear is increased, a point is reached where they begin to flow. This is referred to as the "yield value". When such emulsions are subjected to increasingly higher rates of shear, they exhibit non-Newtonian behavior, and the effective viscosity decreases rapidly until shear rates in the range of 3,000 to 8,000 reciprocal seconds are reached. In this range the effective viscosity plateaus at a figure close to the viscosity of the external phase. As increasingly higher rates of shear are applied, a point is reached where the emulsifying agents can no longer maintain stable films, and at this point the emulsion breaks and cannot be reconstituted readily. The yield value and shear stability point, as well as the shape of the viscosity versus shear curve, will vary with each particular emulsion formulation.

Thus, in order successfully to prepare high internal phase ratio emulsions continuously, it is necessary to employ an apparatus capable of exerting sufficient shear upon the emulsions so that its viscosity approaches that of the phases, particularly that of the external phase, without causing the emulsion to break. While the apparatus maintains the high internal phase ratio emulsion in this state, the phases are introduced therein so as to produce the emulsion on a continuous basis.

In accordance with this invention, there is provided a system for producing at a selected rate a stable, highly viscous emulsion with an internal phase content of at least 75 percent by volume within an immiscible external phase. Supply means provide individual streams of an inverter phase (formed of an internal-in-external emulsifier and an external phase), and an internal phase. First and second flow rate controller means precisely regulate, the flow rates of the separate streams of inverter and internal phases, at a preselected ratio in the range between 95 to 5 and 75 to 25 percent by volume within the system. Mixing means receive the separate streams of internal and inverter phases and distributes stepwise the internal phase progressively in amounts into the inverter phase whereby the internal phase is distributed loosely in the inverter phase. As a result, a composition is formed with the desired ratio in separate components of internal phase, emulsifier and external phase of the desired emulsion. Pumping means move the composition of internal phase and inverter phase at the selected rate. The pumping means also provide continuous shear sufficient to reduce the effective viscosity of the composition near to that of the inverter phase but below the inherent shear stability point of the desired emulsion. The pumping means retain only a minor fraction of the emulsion relative to the volumetric movement of the composition which is converted into the emulsion. The pumping means moves the emulsion to an outlet means which passes the resultant emulsion to a subsequent utilization.

FIG. 1 is a schematic diagram of an apparatus arranged in accordance with the present invention; and

FIG. 2 is a partial sectional view of a flow rate controlling valve employed in the apparatus of FIG. 1.

FIGS. 3 and 4 are illustrations in oblique broken sections of a preferred blender for mixing the external and internal phases prior to their emulsification.

Referring to FIG. 1 of the drawings, there is illustrated a system for producing at a selected rate a stable high internal phase ratio emulsion by a unique combination of readily available elements. In the present description, the emulsion will be described as formed by an internal phase dispersed within an immiscible external phase. For this purpose, the emulsion may be formed of a water phase dispersed within an organic liquid, such as hydrocarbons, or it may be formed of an organic liquid, such as hydrocarbons, dispersed within an aqueous phase. Either type of high internal phase ratio emulsion can be produced by the present system. In each instance, the emulsion will include an emulsifier which provides the proper colloidal environment for the dispersion of a selected internal phase within a selected immiscible external phase. For example, if the emulsion is to be formed of a water internal phase within a hydrocarbon external phase, a water-in-oil emulsifier is employed. If the phases are reversed, then a oil-in-water emulsifier is employed. The present system is without limitations as to the particular material forming the internal and external phases and the emulsifier. These materials are well known and many are listed with U.S. Pat. No. 3,565,817, supra.

The present system includes supply means providing individual streams of an inverter phase and an internal phase. For this purpose the external phase liquid may be carried within inlet conduit 11 to a storage vessel 12. An emulsifier is supplied by inlet conduit 13 to the storage vessel 12 and held therein until required in the process. If desired, the inlet conduits 11 and 12 may be joined by a tee 14. In this manner, the vessel 12 receives the desired proportion of the external phase liquid and emulsifier. The emulsifier will usually be present in amounts of about 1 to 25 percent by volume by external phase liquid employed in the present system. If desired, the vessel 12 may carry a mixer for homogenizing the emulsifier in the external phase liquid. For this purpose, a prime mover 16 interconnects with the vessel 12 and carries a depending shaft 17 upon which are mounted a plurality of shear inducing blades 18. Operation of the mixer homogenizes the emulsifier within the external phase liquid thereby forming the separate stream of the inverter phase which is removed from the vessel 12 through the outlet 19. The internal phase may be obtained from any suitable source and is passed through an inlet conduit 21 into a second storage vessel 22 where it is contained until required for the present process. The internal phase is removed from the vessel 22 by an outlet 23. Although the vessels 12 and 22 are shown to be separate storage containers, obviously they may be portions of a mobile system such as barrels or tanks carried on various prime movers, such as four-wheel vehicles, trucks, fire trucks, and other types of mobile containers. Where the system is to be employed within a stationary facility, the vessels 12 and 22 may be more conventional, such as steel tanks mounted on concrete foundations. Other arrangements will be apparent for providing suitable storage containers for the system depending upon the particular implacement desired.

The flow rates of the separate streams of the internal and inverter phases are precisely regulated in response to pressure changes in the supply sources. For example, the pressure changes within the outlet conduits 19 and 23 may be employed for precisely regulating the flow rates of these phases. In particular, the outlet conduit 19 contains a flow rate controller 26 while the outlet conduit 23 contains a flow rate controller 27. These flow rate controllers are of a specific type which combine the operation of an adjustable orifice and automatic internal regulating valve. These flow rate controllers are commercially available as Kates Automatic Flow Rate Controllers, although other equivalent flow controllers may be used. Broadly, flow rate controllers 26 and 27 can be preset to provide a particular fixed flow rate for inverter and internal phases and will maintain this precise flow rate irrespective of changes in pressure in the outlet conduits 19 and 23 or elsewhere in the present system. The functioning of the flow rate controllers may be appreciated by momentary reference to FIG. 2 where a flow rate controller is illustrated in diagrammatical fragmentary sectional view. The flow rate controller is connected within the outlet conduit 19 and receives a flow of fluid indicated by the arrows 28. The flow rate controller 26 has an adjustable orifice 29 which is provided by cooperation of an arcuate slot carried upon a movable sleeve 31. The sleeve 31 may be positioned relative to the scale indicia 32 to provide any desired orifice 29 to establish a predetermined or preselected flow rate for the particular phase to be regulated above a certain minimum pressure change. Fluid flows through the orifice 29 and passes a regulating valve 33 to outlet conduit 20 in amounts determined by the clearance between the valve 33 and the body of the flow controller 26. This opening or clearance is regulated by a balancing action between a biasing spring 34 and the application of a pressure differential across the orifice 29 applied to a piston 36 carried upon the upper end of the valve 33. A change in pressure differential across the orifice 29 will cause a reflective pressure change above the piston 36. The valve member opens upon a decreasing pressure differential and closes upon an increasing differential. Thus, a pressure rise or fall causes the valve 33 to move and maintain a fixed rate of flow through the outlet conduit 19. Thus, the valve 33 is positioned relative to the body of the flow controller 26 by a hydraulic force balanced by the pressure differential across the orifice 29. This force balancing action maintains constant differential pressure across orifice 29 and hence maintains constant the flow rate determined by the size of the orifice by the responsive movement of the valve 33. Other types of flow rate controllers may be employed if desired which are capable of producing an equivalent function.

The flow rate controllers 26 and 27 are adjusted so that inverter phase flowing in outlet conduit 19 into outlet conduit 20 and internal phase flowing thru outlet conduit 23 into outlet conduit 25 have the desired ratio of the ultimate emulsion to be prepared. For example, the controllers are preset by adjustment of the sleeve 31 so that the flow rate of the separate streams of inverter phase and the internal phase are in a preselected ratio in the range of between 95 to 5 and 75 to 25 percent by volume which can be maintained irrespective of the pressure conditions within the system. This mixing function does not produce directly the desired emulsion. However, the blender 37 provides a distribution stepwise of the internal phase progressively in amounts into the inverter phase thereby forming a loose mixture of uniform composition which can be subject to shear to form the desired emulsion. The blender 37 receives these streams under the fixed ratio conditions provided by the flow rate controllers 26 and 27. The blender 37 has a structure of suitable form to produce this particular stepwise distribution of one phase into the other phase. One preferred structure for the blender 37 is illustrated in FIGS. 3 and 4. The blender 37 comprises a tubular body 38 which has ends carrying the external phase conduit 20, a side inlet 25 for the internal phase, and an outlet 39 to carry immediately the resultant mixture to a downstream pumping device. A plate 41 is positioned medially within the body 38 and contains a plurality of relatively small holes 42, intermediate holes 43, and large hole 44 which communicate transversely within the blender 37. The holes 42, 43, and 44 may have diameter ratios of 1/4 to 1/2 to 1. A portion of the internal phase is received on one side of the plate 41 and passes through the holes to mingle with the external phase received through the conduit 20. Movement of these fluids through the blender 37 causes the internal phase to be distributed stepwise substantially uniformly in progressively greater total amount into the external phase before the resultant mixture reaches the outlet 39. The holes 42, 43 and 44 form mixing stages A, B, C and D, respectively. These holes are spaced into the individual mixing stages and have selected openings to pass the desired amount of the internal phase by consideration of the pressure drops and "C" factors of the holes. For example, the holes forming mixing stages A, B, C and D provide for distributing stepwise the internal phase in total amounts of 50, 65, 82.5 and 85% by volume into the external phase within the blender 37. This arrangement of the holes prevents substantially pure external or internal phases from reaching outlet 39 during operation malfunctions. Thus, the holes 42, 43 and 44 provide a stepwise distribution in geometrically increasing amounts of the internal phase within the inverter phase. As a result, the loose mixture of the internal phase within the external phase in the outlet 39 provides a composition with the desired ratio of the internal phase, emulsifier and external phase of the desired emulsion. However, in some instances this distribution of fluids is unstable and may separate if allowed to remain under stationary conditions. However, in the present system, this composition is then passed immediately to a unique element which produces the desired emulsion.

Although various types of pumps 46 may be employed in the present system, rotary impeller pumps are preferred, and in particular, impeller pumps with rubber rotating members are exceptional in performance. For example, the pump 46 may be a Jabsco rubber impeller pump which is commercially available. This type of pump contains a rotating member 48 carried within its body, and this member carries a plurality of radially extending vanes 49 having an enlarged round tip portion 51. As the pump member 48 rotates, the vanes 49 are readily distended causing the round tip portion 51 to form a substantially effective seal against the body of the pump 46. In addition, the magnitude of shear exerted by the pump 46 upon the composition is sufficient to create the desired emulsion removed through the outlet 47. Usually, the pump 46 is arranged to provide shear rates which should not exceed approximately 10,000 reciprocal seconds which magnitude would cause many high internal phase ratio emulsions to be reverted or broken. Usually, the pump 46 will provide a minimum shear magnitude of about 500 reciprocal seconds. Additionally, the pump must have a prime mover of sufficient power to assure maintaining minimum suction on the flow controllers. Reference to U.S. Pat. No. 3,565,817 will define these operating parameters for the pump 46. Literature is available with various types of pumps and will readily define those that can be employed in the present invention in accordance with the preceding operating parameters that have been defined. The desired emulsion provided by the pump 46 is removed through the outlet 47 and carried to the subsequent utilization.

The subsequent utilization of the emulsions provided by the present system finds many uses in the pharmaceutical, food, cosmetic and firefighting industries. For example, it has been found that high internal phase ratio emulsions wherein the ratio of water phase to a hydrocarbon phase of about 95 to 5 percent by volume produces an exceptional firefighting fluid.

An example of the greatly increased utility of the blender 37 with a perforated divider 41 is as follows: An apparatus of the type covered in copending application, Ser. No. 459,760, was installed on a standard municipal fire department pumper by plumbing it into the booster pump line with appropriate valving. This apparatus had two Kates control valves 27 and 26, respectively, on the water (internal phase) and on the external phase supply lines. The blender 37 did not initially have a separating plate. This apparatus would work successfully in general but occasionally, if the flow of emulsion was interrupted by closing the nozzle at the end of the fire hose, the emulsification process would be disturbed and a cycling of the control valves was necessary to reinitiate operation. The insertion of a plain unperforated divider plate into the blender 37 greatly reduced such occurrences. The installation of the perforated divider plate 41 in the blender 27 permitted interrupted operation and greatly increased stability so that in a subsequent installation it was found possible even to eliminate the water line Kates control valve and substitute a manual control valve at this point thereby reducing the weight and the cost of the apparatus.

Subsequently, an apparatus like the above equipment was operated so as to produce an oil-in-water type of high internal phase emulsion for fuel test purposes. Again, it was found unexpectedly that the installation of the perforated divider plate 41 within the blender 37 greatly increased the ease of initiating emulsion production and permitted production without startup difficulties.

The present system avoids the difficult and sensitive controls needed for precise metering and pumping mechanisms and in the operating of high shear mixing and emulsification devices, which have led in the past to complex sensitive, nonportable and difficult to operate continuous emulsification systems. The present system is an invention which avoids all of these problems encountered by known continuous emulsification apparatus.

Various modifications and alterations in the described system will be apparent to those skilled in the art which do not depart from the spirit of the present invention. For this reason, these changes are desired to be included within the scope of the appended claims. The appended claims define the present invention; the foregoing description is to be employed for setting forth the present system.