What equipment is necessary for chemical mixing?

This is a very broad question, so let’s try to break it down and organize it. The first question that we need to ask is, “What is the purpose of this chemical mixing?”
Depending on the process, we will be able to select the appropriate equipment. If we’re talking about blending materials and we use blending equipment, then that is doing blending, it will not extremely diffusivity dependent, it will only moving the material in some time, and if the material will be stable, it will be enough. If we’re talking about complex phenomena, that is, reactions, crystallization, fermentations, or two-phase mixing, then we need to take into consideration another level of mixing, which will again depend on the process.

For instance, for two phases that are not miscible or liquid phases that are immiscible, if we apply a high shear rate, then we will generate an emulsification that is stable and once the stirring stops the materials cannot be separated. This is useful to produce creams, ointments, and similar formulations. When we talk about the same kind of a situation, e.g., liquids that are not miscible, and we want only to move them well, i.e., mix but not emulsify, then we need to use mixing equipment like mixing tank with a low shear rate but that generates enough intensity to create drops in the continuous phase to transfer material from phase to phase. So, it is this kind of issue that requires more specific knowledge about the process. We have in the software a table that we also include in this paper that discusses the connection between mixing equipment and the mixing parameters that influence particular processes. In the end, these are very local questions and the answers vary depending on the project under consideration. In conclusion, mixing is always a unit operation that services a particular process; in other words, one type of equipment can be good for one process and very bad for other processes. The only way to choose the right type for given parameters is to have a good understanding of the process, the materials, and the desired result and of course a good mixing software.

Examples of Solid-Liquid Mixtures

After we elaborate on the meaning of solid-liquid mixture, we can explore some of these mixtures that can be utilized in the industry and generally in typical process activities.

Primarily, there are two main classes of solid-liquid mixtures. The first type is a solid-liquid mixture in which the solid is first partially dissolved in the liquid phase. Subsequently, by some compounding or consumption, this solid wheat reduces its size until it disappears. The mass transfer coefficient will determine this transfer to the liquid phase by solubility and consumption with other reagents. Here, we may confuse the reaction rate with the mass transfer rate. Therefore, the best way to comprehend whether we are on the mass transfer control or the reaction kinetic or biological kinetic process is to vary the agitator’s RPM. Because once we alter it, the main change will occur to the mass transfer coefficient. As a result, detecting that the reaction rate is different implies that the mass transfer will control the process. On the other hand, if we change the RPM and continue to observe the same reaction rate or the same distribution of materials’ quality, it implies that the process is controlled by the chemical kinetics or the materials themselves. In this case, mass transfer is not a part of our considerations. This typical example illustrates how to use solids in very specific processes.

The second type of solid-liquid mixture offers practical examples that are entirely different. In this case, we have solids in our liquid media and aim to have some distribution of solids in our tank, but this solid is undissolved. In this case, the solid keeps the same size, and only its presence in all the equipment is essential. For instance, in the case of heterogeneous catalytic reactions where the catalyst is solid, it does not change its composition or size and is not dissolved in the media. It is only the place where the material meets and reacts. Of course, this sort of activity is frequently required, characterized by a mass transfer rate. Consequently, some distribution of solids will be required for the process control. However, in this case, we are not talking about the mass transfer from the solid to the media, but the very good distribution of solids and some conditions around the catalysts and the solids that provide a good diffusivity of the reactants into the catalysts to react. Thus, we can observe two entirely different kinds of processes that can be perplexing, as they will control completely different types of results. We can evaluate these outcomes by combining good mixing calculations into the tank with Visimix. Furthermore, these results, combined with the real conditions will apply in some places, such as labs, previous equipment, or new equipment. As a result, based on these real outcomes and the mixing environment we provide, we can decide the most optimal way to progress and improve our capability to produce outstanding results. We have observed that we must need some solids suspension in several daily materials in the pharmaceutical industry or typical fine chemicals used for domestic products, such as eye or nasal drops or facial creams. It is the foremost priority before actualizing chemical reactions or biotechnology. The solids suspension is the outcome of these complex processes at industrial levels. For this purpose, we always look for material homogenously in every final dosage we offer to our customers.

However, the primary question is, what will be the distribution of the solids? It is very simple. These kinds of materials—creams, ointments, and slurries—are characterized by very small particle sizes. Primarily, they are provided in a laminar regime, so their viscosity is very high. Therefore, we must understand the hydrodynamic and mixing process parameters controlling the solid distribution.
All the above examples characterize the behavior of the solid in our processes. Of course, we have not discussed the vessels’ role, as it is not our field.

Nonetheless, as I explained above, we must incorporate the interaction between the materials. Thus, we should cautiously consider the compatibility of the material with others to fulfill our main objective in a reaction or formulation. Furthermore, it is pertinent to say that it is not about the conditions provided to the processes through operation and steering but the chemical and physical characterization of each material and its compatibility with others.
Finally, this discussion is not part of the ultimate mixing outcomes, but it is about the input data to compute the mixing of materials required for a certain process.

VisiMix Video

The Influence of Mixing in the Process
New methodology using VisiMix software for the purpose of checking the influence of mixing in the processes.

VisiMix Demo Operation
Learning how to input data into the VisiMix software and get results the will help us understand the influence of mixing in our processes.

Lab Experiments
Learning how to set up the relevant experiments at the lab scale, to develop the processes from an engineering point of view.