I'd say it depends on what you want to do: if you want to compare chemical states before and after the reaction, calculating the chemical equilibrium is sufficient, so you won't need formations rates. If on the other hand you want to describe the temporal evolution of the chemical reaction, the you need to calculate the formation rates of the various involved species.

The question was partly provocative. In it I wanted to oppose the mass balance of processes in various systems (batch, semibatch or flow) to formal definitions of reaction rate. As far as the current process rate in a particular reactor type is concerned, it is enough to determine the dependence of a given current variable (concentration, conversion, etc.) from the time or space time (solution of mass balance equation/s) and to differentiate it. Regards,

In order to design a chemical reactor you need to know something about twhat's going on inside the reactor . Using a kinetic reaction rate constant and thermodynamic information is a reasonable way to do that but it is not the only way. People have built reactors that work via trial and error without kinetic models with little or no understanding of the science for a very long time. However it is usually much easier to do it well if you have some understanding of the kinetics and the thermodynamics.

Nowadays, without knowledge in the field of stoichiometry, thermodynamics and kinetics, little can be done in the the design of process in reactor. However, how the relationship between reaction rate and process parameters will be determined, a formal definition of reaction rate is not needed. It determines the mass balance. However, was such a need in the past? Of course not. Many years of experience was enough.

Misoslaw, You are pobably correct for most large scale plants but I'm pretty sure there are still dsome small chemical plants making products like paints, adhesives and various polymer blends that will add a little bit of. this or that to see if it helps and blend off any offspec material as necessary.

Rick, You are fully right, which also results from your professional experience. Producers on a small scale, not only do not know what kinetics is, but also stoichiometry. Why do they need it? They buy the installation with know-how and the quality of the product/s is important to them. But in this way, we have departed from the subject of the question. Regards,

Much empirical data was collected in the past. To improve a process the reaction rate must be expressed symbolically and in agreement with the data. In this way the mechanism can be deduced, and proposals can be made for testing.

There are many sets of kinetic data and many equations (kinetic equations) describing them. Unfortunately, a large part of them are equations, with so-called lumped parameters. Such equations are useful in the design of reactors, but unusable from the point of view of the process mechanism. A good fit is not enough to conclude about the mechanism. But again, we left the question. Regards,

Miroslow,

In the refining industry "Lumped" kinetics is necessary because of the large number of components in crude. Lumping into a managable number of cuts ( 5-10) and characterizing each cut based on average boiling point gravity, Sulfur,Nitrogen and sometimes conradson/ramsbottom carbon is a necessary shortcut.

Refineries often operate with only occasional Sulfur, and gravity measurements performed once a day or someimes as long as once month, It is extremely rare for a refinery to ever get ac omplete compound by compound analysys of the material they' re running ( I think I saw an Exxon refinery attached to a research facikity do this once)

Reaction mechanism studies are sometimes done in lab scale pilot plant reactors. Lumping is still required but narrower cuts are used and more anlysis are performed for these studies. For example it is well know the Dibezothiophenes are significantly more difficult to hydrotreat when they are beta-substututied but this information isn't usefull to the typical operator because thet never measure it.

I agree for pure research purposes undersatnding the exact composition of a feed is highly desirable. But sometimes you can't get it so you haveto make do with the data that you can actually get.

Rick, I fully agree with what you wrote. The industry and the university laboratory or room are two different worlds. One is about intensification, quality and profit, while in the second "world" science is developed. I am an academic teacher and I teach students. In industry, I was a trainee for a total of about one year. It's nothing compared to your professional experience. But that was not the issue that concerned the question. Although here I made a mistake, it should be a discussion, not a question.

As for the question, it has a hidden meaning. I wanted to pay attention to the difference between the rate of the chemical reaction/process (as in definition) and the mass balance or in general balance. These terms are often confused and unintentional mistakes occur. I could describe a number of such situations here, e.g. based on papers on adsorption. But maybe someone else, something more will write. Regards,

Miroslaw, Science is sometimes developed in industry but it is usually by accident. The delayed coking process was allegedly discovered when an operator lefy hot oil in a drum too long then openened it up to discove cracking and coke formation had occurred. There are a few real scientists doing fundamental research in industry but they are usually more focused on making money then the actual science.

Rick, There are a lot of science in idustry. There is DSM chemical plant. There is DSM Reseach Centre (once I was there). The point, however, is that most of the achievements are classified. Knowledge costs a lot. Regards,

I missed this discussion. I guess it's not too late to join it.

First, the clear definition of each term is absolutely necessary. Therefore, let's first define what is the "reaction." Commonly, we describe a reaction by an equation such as aA + bB + cC... ->... xX + yY + zZ. This is also called the reaction stoichiometry, mass balance, or whatever else. We define the reaction rate as the change of a total number of molecules of one of a reagent with time. If you select another reagent/product, the value of the reaction rate will be different. Whatever reagent/product you choose, all rates are linked to each other by the reaction stoichiometry (mass balance). In other words, the term "reaction rate" does not make much sense if you don't write the reaction equation. However, in certain cases you don't need to know the reaction equation. For instance if you interesting just in one reagent, e.g. A -> product(s), then the rate is dA/dt. I'm not a chemical engineer and can't answer the original question.

Yurii, It's very nice that you join the discussion that I started. Unfortunately this week I'm out so I will write nothing. But maybe someone else will join. I also hoped that somebody involved in the kinetics of sorption processes would join, unfortunately no-one joined.

The topic of the discussion was not precisely formulated, hence I added additional explanations. But as usually happens, we have gone away a few times from this topic. I do not think, however, that one should consider here what the chemical reaction is and how it can be written down. Moreover, speaking of rate in the sense of definition, rate equation (for me kinetic equation) and balance equation/s, for example, mass balance equation/s I do not have to refer these concepts to chemical reactions. However, in my opinion, chemical reactions are a good reference for the description of other processes and phenomena. Regards,

From chemical reaction engineering kinetics the order of the reaction is dependent on volume of reactor and the reaction is to be considered as constant

volume or constant pressure . There are different types of reactors depending upon the type of reaction used ie liquid / Gas phase and accordingly reactor will

be classified as Batch , CSTR / PFR type of reactors .