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Process for forming an emulsion using microchannel process technology

Process for forming an emulsion using microchannel process technology description/claims

This application is a continuation of U.S. application Ser. No. 10/844,061, filed May 12, 2004, which is a continuation-in-part of U.S. application Ser. No. 10/440,056, filed May 16, 2003. This application also claims priority to U.S. Provisional Application Ser. No. 60/548,152, filed Feb. 25, 2004. Each of these prior applications is incorporated herein by reference in its entirety.

This invention relates to a method for making an emulsion using microchannel process technology.

Emulsions may be formed when two or more immiscible liquids, usually water or a water-based solution and a hydrophobic organic liquid (e.g., an oil), are mixed so that one liquid forms droplets in the other liquid. Either of the liquids can be dispersed in the other liquid. When, for example, oil is dispersed in water, the emulsion may be referred to as an oil-in-water (o/w) emulsion. The reverse case is a water-in-oil (w/o) emulsion. More complex emulsions such as double emulsions may be formed when, for example, water droplets in a continuous oil phase themselves contain dispersed oil droplets. These oil-in-water-in-oil emulsions may be identified as o/w/o emulsions. In the same manner a w/o/w emulsion may be formed.

A problem with many emulsions is that if they are not stabilized, for example, by adding surfactants or emulsifiers, they tend to agglomerate, form a creaming layer, coalesce, and finally separate into two phases. If a surfactant or emulsifier (sometimes referred to as a surface-active agent) is added to one or both of the immiscible liquids, one of the liquids may form a continuous phase and the other liquid may remain in droplet form (“dispersed or discontinuous phase”), the droplets being dispersed in the continuous phase. The degree of stability of the emulsion may be increased when droplet size is decreased below certain values. For example, a typical o/w emulsion of a droplet size of 20 microns may be only temporally stable (hours) while that of one micron may be considered as “quasi-permanently” stable (weeks or longer). However, the energy consumption and the power requirement for the emulsification system and process may be significantly increased for smaller droplet sizes when using conventional processing techniques, especially for highly viscous emulsions with very small droplet sizes and large outputs. For example, the doubling of energy dissipation (energy consumption) may cause a reduction of average droplet size of only about 25% when using conventional processing techniques. Shear force may be applied to overcome the interfacial tension force and in turn to break larger droplets into smaller ones. However, as the droplet size decreases, the interfacial tension required to keep the droplet shape tends to increase. Energy consumption may take place in various forms, for example, it can be the energy needed by the stirrer to overcome shear force of the emulsion in a batch process, the energy for heating and cooling, and/or the power to overcome pressure drop in a continuous process such as in a homogenizer. Heating is often needed for emulsification when one of the phases does not flow or flows too slowly at room temperature. A heated emulsion typically has lower stability, however, due to lower viscosity of the continuous phase and in turn less drag. Drag may be necessary to stop or resist the motion of the droplets and in turn the coalescence into larger and often undesired droplets or aggregates of droplets as well as phase separation into layers. After emulsification, droplets tend to rise by buoyancy. As such, an immediate cooling down may be needed, which also consumes energy.

A problem with many of the processes that are currently available for making emulsions is that the range of compositions that are feasible for formulating product are constrained. For example, a problem with many of the emulsions that are currently available relates to the presence of surfactants or emulsifiers in their formulations. These surfactants or emulsifiers may be required to stabilize the emulsions, but may be undesirable for many applications. For example, heating without bubbling or boiling is often desired in emulsification processes, however in some instances the onset temperature of nucleate boiling or air bubble formation from dissolved air in the continuous phase may lower when surfactants or emulsifiers are present. Boiling may cause unwanted property changes. Air bubbles may cause creaming and other undesired features.

Emulsions that have low surfactant or emulsifier concentrations or are free of such surfactants or emulsifiers are often desirable for skin care products in the cosmetic industry. A disadvantage with some surfactants or emulsifiers is their tendency to interact with preservatives, such as the esters of p-hydroxybenzoic acid, used in skin care products. Skin irritation is another problem often associated with the use of surfactants or emulsifiers. Many adverse skin reactions experienced by consumers from the use of cosmetics may be related to the presence of the surfactants or emulsifiers. Another example relates to the problem with using surfactants or emulsifiers wherein water proofing is desired. For example, in water-based skin care products such as sunscreen, the active ingredient may not be waterproof due to the presence of water-soluble surfactants or emulsifiers.

A problem relating to the use of many pharmaceutical compounds relates to the fact that they are insoluble or poorly soluble in water and there are limitations as to the surfactants or emulsifiers that can be used. This has resulted in the discovery of drugs that are not clinically acceptable due to problems relating to transporting the drugs into the body. Emulsion formulation problems may be problematic with drugs for intravenous injection and the administration of chemotherapeutic or anti-cancer agents.

The present invention, at least in one embodiment, may provide a solution to one or more of the foregoing problems. In one embodiment, it may be possible to make an emulsion using a relatively low level of energy as compared to the prior art. The emulsion made in accordance with the inventive process, at least in one embodiment, may have a dispersed phase with a relatively small droplet size and a relatively uniform droplet size distribution. The emulsion made in accordance with the inventive process, in one embodiment, may exhibit a high degree of stability. In one embodiment, the emulsion made by the inventive process may have a low surfactant or emulsifier concentration or be free of such surfactants or emulsifiers. The emulsions made in accordance with the inventive process, in one embodiment, may be useful, for example, as a skin care product, pharmaceutical composition, etc.

The invention relates to a process for making an emulsion, comprising: flowing a first liquid through a process microchannel, the process microchannel having a wall with an apertured section; flowing a second liquid through the apertured section into the process microchannel in contact with the first liquid to form the emulsion, the second liquid being immiscible with the first liquid, the first liquid forming a continuous phase, the second liquid forming a discontinuous phase dispersed in the continuous phase. In one embodiment, the second liquid flows from a liquid channel through the apertured section.

In one embodiment, heat is exchanged between the process microchannel and a heat exchanger, the liquid channel and a heat exchanger, or both the process microchannel and the liquid channel and a heat exchanger. The heat exchanger may be used for cooling, heating or both cooling and heating. The heat exchanger may comprise a heat exchange channel, a heating element and/or a cooling element adjacent to the process microchannel, the liquid channel, or both the process microchannel and the liquid channel. In one embodiment, the heat exchanger may not be in contact with or adjacent to the process microchannel or liquid channel but rather can be remote from either or both the process microchannel and liquid channel.

In one embodiment, the first liquid and the second liquid contact each other in a mixing zone in the process microchannel.

In one embodiment, heat is exchanged between a heat exchanger and at least part of the process microchannel in the mixing zone.

In one embodiment, heat is exchanged between a heat exchanger and at least part of the process microchannel upstream of the mixing zone.

In one embodiment, heat is exchanged between a heat exchanger and at least part of the process microchannel downstream of the mixing zone.

In one embodiment, the emulsion is quenched in the process microchannel downstream of the mixing zone.

In one embodiment, the process microchannel has a restricted cross section in the mixing zone.

In one embodiment, the process microchannel has walls that are spaced apart and apertured sections in each of the spaced apart walls, the second liquid flowing through each of apertured sections into the process microchannel. In one embodiment, the apertured sections in each of the spaced apart walls comprise a plurality of apertures, the apertures in the apertured section of one of the walls being aligned directly opposite the apertures in the apertured section of the other wall. In one embodiment, the apertured sections in each of the spaced apart walls comprise a plurality of apertures, at least some of the apertures in the apertured section of one of the walls being offset from being aligned directly with the apertures in the apertured section of the other wall.

In one embodiment, the process microchannel is in an emulsion forming unit comprising a first process microchannel, a second process microchannel, and a liquid channel positioned between the first process microchannel and the second process microchannel, each process microchannel having a wall with an apertured section, the first liquid flowing through the first process microchannel and the second process microchannel, the second liquid flowing from the liquid channel through the apertured section in the first process microchannel in contact with the first liquid and through the apertured section in the second process microchannel in contact with the first liquid.

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