Chemical reaction simulation

Chemical reaction simulation is mainly a tool based on physical models that are expressed by mathematical differential equations, normally ones that are very nonlinear and complicated to solve. The only way to solve them is by numerical methods.

The physics that express the differential equations of these models, and their results, should represent the progress of the chemical reaction that is happening in some kind of operation. The typical operation in the chemical industry is batch or semi-batch operation for fine chemicals, for chemical specialties. For mass development of products, we are talking about continuous flow. The tool of chemical reaction simulation helps the industry predict what the results of the chemical reaction operation will be, and to generate results that will be the basis for design, sorted problems, and transfer of products to the next phase—size or scale-up—or for the next facility. Chemical simulation is the tool, and it can be used in many areas. The point is that the reaction simulation should be a good one, a representative one, and should take into consideration the physics or interaction between the materials during the movement and mixing. It should also take into account the reaction rate, the chemical affinity between the materials. When we combine these parameters, we’ll be able to generate results that are representative. Some errors may continue to occur, because with any simulation or calculation, intrinsically, we have some errors. But the answer will be in the range of magnitude that we expect to happen; it will be enough good to be representative of our next step and decisions.

How do you define this in simple terms of no expense? It’s like a calculator. It’s like every exercise you did in university when studying a topic. For instance, if you want to solve an equation involving unknown variable x, you complete all the arithmetic activities to discover what the value of x is in the equation. Here it is exactly the same, but the mathematics is a little more complicated because physics is involved; the level is completely different. But in basic terms, the operation is like a calculator. It’s like applying what you knew to solve simple exercises that you did for every topic you studied in university—except with more sophisticated tools.

What are the core principles and underlying terms? We have here too many important kinetic and thermodynamic considerations. The first is that we have materials that are chemicals. Under certain conditions, those chemicals will react, interacting with each other and, as a result, generating a new material. What is a new material? It has different physical properties than the original material. This is the result of the chemistry, which can change even in a very deep study of physics by quantum theory and energies, etc. But, in fact, when we put these two materials in contact with each other, they will react and generate a third material that is not similar to the first or second one.

The second consideration is that materials have different levels of energy. In every system in the world, all materials would like to exist in as low an energy level as possible. Reactants have their own energies, and the resulting product has its own energy as well; the reactants want to become a product because their energy levels are not stable. So, the energy of the product is lower than the energy of each of the reactants under the conditions we have. And of course, we must understand that we need some starting energy to get our reactant materials to interact with each other; this is called the energy of activation. So, there is the minimum energy required for the materials to interact chemically and enact an exchange in electrons, whatever, to generate a product that is more stable.

So, this is the thermodynamic consideration. When we talk about kinetics, however, the common questions are: What will be the time required to generate this interaction? How long will it take this interaction to generate the product? Here, we discover the influence of mixing. Why is mixing so important? Because the interaction between materials should be done by some movement of material. When we have materials that are moving—that is, mixing—we generate some kind of rate of interaction between the materials, which, under the chemical conditions, will exchange electrons and generate our product.

So, we have the kinetics of the interaction between the materials, and we have the kinetics of the chemistry by itself. These are the main principles we use to understand and manage the electron transfer from one material to the other, which generates our product. But if we consider the situation realistically, we will see that inside our tank and under our conditions, there is competition between the capability of the materials to transfer electrons and the capability of the equipment to generate the interaction between the materials. The interaction between the materials is slower than the capability of the material to transfer electrons (this is chemical kinetics), so the chemical process will be controlled by the mass transfer, by the mixing. But if the mixing is very fast compared to the capability of electron transfer, the process will be controlled by the chemical kinetics. And our mission in the industry, in this field, is to try to identify the kinetics in different configurations of equipment and under different conditions for chemical reactions.

Chemical kinetics is a function of temperature and concentration. It is a pure chemical situation, and the mass transfer of the mixing conditions is a function of the velocity of the flow, the flow patterns, and the intensity of the mixing in different places in the tank. We should understand what main control regime we use to manage the mixing rate or mass transfer, in comparison to the chemical kinetic reaction.

The last question that we’ll answer now, and maybe discuss further next time, is this: What kind of data does the chemical reaction simulation utilize? Our data collection comes from two sources. The first source is to change the concentration and temperature of the reactant; this will generate the reaction kinetic constant that is mainly associated with the reaction kinetic rate and the order of the reaction. We collect this information by taking samples of the reaction mixture as the reaction is progressing. Once we finish taking 5, 10 or 20 samples of the concentration as a function of the time during the reaction, we will be able to know what the kinetic reaction rate is. If we change the temperature and evaluate the same process with the same concentration, we will be able to know what the energy of dissipation is. That is the second parameter that will define the kinetic reaction rate. Of course, this should be done at the same mixing rate of rpm. It should be done with the understanding that the mixing is faster than the reaction in order to catch the reaction rate coefficients and the order of the reaction rate. And with this, we’ll finish discussing the first mechanism to be characterized.

The second mechanism, the mass transfer of the mixing intensity, is done by changing, under the same conditions, the rpm instead of the temperature. If we see some deviation, we will be able to generate some connection regarding the intensity of the mixing, the mixing time at different levels, and the reaction rate. Utilizing both mechanisms is possible through our VisiMix Chem software, which builds on our mere physical models that consider the constraints of the chemicals and mixing. The software also assesses what lower and maximum limits of mixing are possible according to the reaction. Whatever answer is provided will have taken into consideration the fact that it is impossible, from a physics point of view, to put a molecule in front of a molecule. What we are normally doing when mixing is putting a group of molecules in some small space; they then interact by diffusivity. We take into consideration the reaction rate and macro mixing time—the time to generate 99% homogeneity—and we compare this with the reaction rates. We provide to you some ideal mixing, some ideal concentration of product and reactant needed for 99% homogeneity, and we take into consideration the lower level of constraint—that is, the fact that it’s impossible to put one molecule in front of a second one—when producing the actual mixing results. Sometimes the results will be similar, sometimes they will not; when they are not similar, this means that the local mixing, the level of molecular mixing, or the fluid element mixing is controlling the process.

So, we’ve finished addressing the first four reactions that provide a very good explanation of the principles of chemical reaction simulation on the mixing environment. And of course, we can continue to discuss this with regard to different opportunities. For instance, what are the primary goals of learning simulation? Why is chemical reaction simulation so important? Of course, the answer is clear: to reduce cost. All of this takes us to interaction, of course—a serious topic that will be completely different. What is the safety? The chemical should be the material we need to control, from the point of view of reactivity. We need to control the reaction so it does not develop into an uncontrolled situation that may generate due to an accident, such as a fight or explosion or detonation. To avoid such a situation, we must consider these two fields and try to coordinate between them.