Rotor-Stator Disperser

A rotor-stator disperser is a piece of equipment that provides us the capability to increase dramatically the shear rate that we apply in our media. The main use of rotor-stators in the industry is to generate homogenization, typically to generate emulsifications. Products like creams and ointments are a common result of this process, and the use of rotor-stators is frequent in the industry. The VisiMix rotor-stator is the first practical model you can find in the market, allowing companies to try to configure the capability to generate emulsification at different levels and in different sizes from the lab to production.

This VisiMix RSDE give us the capability to calculate a unique shear rate when using the rotor-stator with other equipment. If the order of magnitude of the shear rate in a normal agitated equipment is about 1,000s frequency of the shear rate, the rotor-stator provides about one or two orders of magnitude higher than the normal capability of the sterile vessel to generate the shield rate. The point is that this is local; this is an addition to the sterile vessel. The main activity that happens is that the sterile vessel generates some kind of starting-point homogeneity—that is, in the macro—in fluid elements that are bigger. And when we start to apply the rotor-stator, we are feeding this material in a homogeneous way to the rotor-stator place. Around this rotor-stator, we’re generating the high shear rate and very, very small fluid elements that can produce more drops and result in the emulsification that we’re looking for. So the activity of the rotor-stator is local. The software is able to calculate the main, important parameters that happen in the fluid, like shear rate, the specific power that we’re applying to our media inside the rotor-stator, the pumping capability, and the power needed to design the equipment for companies that manufacture it for our capabilities.

The third typical mistake is that we assume that in the laboratory we have a perfect interaction between the materials, so the mixing is ideal. So, it is exactly the opposite. Normally when we are in the lab, because the dimensions of the equipment are small, 0.5 l, 1 l, 250 ml, the dimensions of this equipment generate interaction between the materials that are very close to a laminar regime. So, it’s a full capability to interact between the materials. When we go to the big equipment, the capability to interact between the materials is better because we are in the turbulence regime, and in the turbulence regime, the capability to have a good interaction between the materials is higher. So, when we are coming to very low Reynolds numbers, meaning of this laminar regime, the interaction between materials is not so representative of what we will have after that in the production step. And all these deviations in the interaction between materials will generate maybe different kinds of phenomena that are happening into the process that will not happen in the next step because we are not in the same regime of work. This is the third one.

And the fourth one is more some kind of intuition. For instance, we’re talking about exothermic reactions. The small equipment has a lot of surface per volume, and we are able to transfer heat in a very effective way. So, if we are working in the lab and my equipment is growing in temperature let’s say by 10 degrees during the reaction in the lab, the meaning of this, is that when we go to the production, when we have order of magnitudes less surface per volume, the meaning of this is that the capability to transfer heat to the jacket will be lower, so we are close to adiabatic systems. And when we have adiabatic systems, the temperature will grow fast and will be bigger. And this can confuse us, and maybe we think that our process is not exothermic or is not a problem of exothermic, but when we go to the next step, it will be really a big problem, because we are not able to extract all the heat from the equipment.

The other point that continues to be a phenomenon, is, we assume that when we have homogeneity in our tank, the process will always be good. And this is not true. The process requires some interaction between the materials. And not always when we have a good interaction between the materials, we are generating results that are good for the process. A very simple example. For instance, when we have two liquid phases that are not miscible and we have a process, for instance, emulsification, we will like to generate emulsification, so oil drops that will be small enough that will not separate after we stop the mixing. So, this is emulsification, creams, and ointments. And for this, we need a high shear rate. We need high velocity, high shear rate, we need homogeneity. And if our goal will be different with the same materials and the same equipment, we need only to transfer material from one phase to another phase. And after that, when we stop the mixing, separate phases, it will not happen, because we have a very good mixing and the meaning of this, it will not separate. And for us, we will be very, very proud. Or another example, we have a reaction that is a fast reaction and is controlled by mass transfer. If we are applying a high velocity, maybe we will promote a secondary reaction that is not good for me, it has generated some impurity, and we are losing the productivity and the quality of the end material. So, in this case, when we have homogeneity, maybe it’s not good. So, the assumption that good mixing is equal to good process is a common mistake, and it is not a good approach. And like this, we have other kinds of conclusion that we can think about then, for instance, mixing times that will not be exactly the same mixing times in the lab and the production step or we assume that when we have a very big vortex, the meaning of this is good mixing and it is good for the process. All of this assumption is not good. Opposite normally, when we have a very big vortex, the meaning of this is that we have no capability to have interaction between the materials, and at least more and more.

So, it is very important to take in consideration that we have two main fields; the chemical affinity between the materials, that is the reactivity, solubility, gas consumption, etc., and the physics. So, what are the conditions we’re providing in our materials to progress with the process, and how is the connection between these two main fields that happen in the tank anyway, because normally we’re manufacturing our process into the sterile vessel, and we need to take care of it. So, hydrodynamics separately and chemistry separately is good only to understand, but after that, if you want to go to optimization, the goal is to have good conditions in the productivity state, in the industry stage, we need to connect between them, and we need to understand how is the interaction between these two main phenomena that happen into the sterile vessels.