This device is used in many industries for different purposes. The main idea or fundamental use of this device is to generate a local high shear rate or higher shear stress. In our equipment, this device produces a shear rate that is 1–2 orders of magnitude larger than the shear rate generated with a normal standard steel vessel with different kinds of agitators, including radial agitators.
The rotor–stator homogenizer generates a local high shear rate that can be used to create stable emulsification by accelerating the mass transfer rate. Turbulence diffusivity or hydrodynamic diffusivity plays a highly significant role in all biotechnology processes.
I will begin with the primary application of this device, which is to generate a high shear rate in order to induce emulsification. Emulsifications are mainly used in the cosmetics industry, where we want to generate some creams; i.e., water/oil compositions or ointments that comprise two immiscible organic materials. These materials require a high level of shear stress that is not achievable with standard stirrer vessels and agitators. Hence, we introduce in our stirrer vessel a simple rotor–stator homogenizer.
The secondary use of this device is for creating a wet meal, meaning to reduce the particle size of the solids, but not in a dry phase and not the powder by itself. The process involves feeding the solids into a liquid medium and then transferring this slurry through the rotor–stator homogenizer. Because we are applying a very high shear rate, we are able to reduce the particle size, i.e., wet milling. Other uses include processes that involve very fast reactions. In this case, in a normal stirrer vessel, the process is controlled by mass transfer.
Once we introduce our rotor–stator homogenizer in a stirrer vessel and generate shear rate and energy of dissipation at two orders of magnitude more, a high level of diffusivity is achieved, which reduces the capability of materials to meet between two regions and generate a reaction. This improves the main reaction and, hopefully, secondary reactions will be sufficiently slowed to allow finalizing the product. This method is common in the biotechnology industry. For example, as a result of the growing quantities of cells in our tank during fermentation, and in order to extract the material from the cells, we need to rupture the cell membranes. This can be done by applying a higher shear rate than we are able to do with the rotor–stator homogenizer.
In summary, the rotor–stator homogenizer allows us to generate shear rates that are 1–2 orders of magnitude higher than in normal stirrer vessel equipment.
The rotor-stator homogenizer is a device that is used mainly in the formulation industry to generate homogeneity at a high level. This equipment can “cut” the fluid into very, very small parts, microns and less-than-micron parts. And when you have very small parts that are moving in time, you’re able to generate a high level of homogeneity. The physical parameter that describes this activity—and the number you can use to know the level of coating you’re doing in your tank with the rotor-stator device—is the turbulent shear rate, or shear stress. This is mechanical equipment: in the center we have a rotor that is moving very, very fast: 20,000 RPM. We have a stator that is static—it’s not moving—and the distance between the rotor and the stator is between 0.5 mm and 5 mm. Thus, the main shear rate is happening between the rotor and the stator.
Why is this equipment important, and why is it used? In the beginning, it was used because to generate emulsification for two liquids that are not miscible and are generating two phases.
We need to generate drops. Once the drops are very, very small, the material is unable to coalesce again and generate two phases. This is the basis for the creams or ointments we use for pharmaceutical reasons, and even only to protect ourselves from the sun in the summer or when we go to the beach.
The rotor-stator can generate very small drops that will generate the emulsification that we use. In the same way, this kind of rotor-stator can break up solids. So, we have agglomeration of solids moving the tank, and when we apply this rotor-stator to separate these agglomerates into very, very small particles—only microns to very few microns—we will be able to generate some kind of slurry, some kind of suspension that will not precipitate and will have a good composition of material and formulation. This is another kind of material that we’re using in the final dosage in materials that are for injection. The material inside consists of small particles; it is not even dissolved but is presented as a suspension of particles.
This kind of equipment is able to generate small parts in a flow, and because the parts are very, very small, we’re able to generate a high level of homogeneity. Even for soluble material—one liquid in another liquid, or solid in other form in a liquid—the equipment will accelerate the time required to generate full dissolution of the material. A lot of this is happening, but why? Because this equipment can generate this shield rate, this number, this coating level by one, two, or three orders of magnitude more than we are able to achieve when we have a normal steered vessel, or a normal agitation in the tank. This is the main advantage of this kind of equipment. The rotor-stator homogenizer can generate very small parts in the tank and accelerate the homogenization of the material in the tank by circulation and more, because there is no other way to generate these kinds of activities with the normal steered vessel that are used in the company.
Now, the rotor-stator homogenizer is used in the cosmetic industry, formulation industry, and dye industry. So, it is a very popular equipment and is the head of the application for these kinds of companies because they are doing compounding, and normally the final product of these companies is some kind of paste, cream, or other material normally having a high level of viscosity. And to achieve this level of viscosity, we need equipment that will be able to move the material, even if the viscosity is very high, and will continue to apply the force required to generate homogenization. This is on the one hand.
On the other hand, maybe we can use the rotor-stator in all fields, and we can speak about the connection between the rotor-stator homogenizer and chemical reactions. So, we can elaborate after that, but what we’re saying for now is that because we are able to generate very small fluid elements into the media—because this equipment generates a high shear rate—we’re able now to generate a very good connection between the materials. The interaction will be very, very thin, in the order of microns and less. So, we have more connection between the reactants and the reactions. The mass transfer will be so fast that maybe we will only depend on chemical reaction rates. Or, we will control the process when the reaction is instantaneous, and we will be able to control the process with the rotor-stator, but the rotor-stator will be enough for us to generate the main reaction and avoid secondary reactions. We can elaborate on this in another paper, but regarding the rotor-stator homogenizer, the quality of this device allows us to control very fast reactions and continue to generate materials that we’re looking for, because we know the connection between the environment, we’re generating our materials to interact in and the result we’re looking for.
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