Currently, I can see thousands of studies doing TGA pyrolysis and gasification. The obtained TGA data is frequently used to conduct Kinetics such as Activation energy, pre-exponential and reaction rate etc. But none of the papers have mentioned answers of following questions:
Why do we need to do kinetics? how does their results will help to up scale the pyrolysis or gasification processes towards reactor?????????
It depends how simplified or complex the kinetic model is. For example if one assumes a linear weight decrease for calculating Activation Energy and Pre-exponential factor, this is usually used to compare the reactivity of different fuels under the same conditions. The former concerns the minimum energy to start a reaction, whereas the latter concerns the amount of reactions per time.
It depends on what your purpose is. Mankind has known how to burn wood and other biomass for a very long time without the aid of any detailed analysis of the nature of combustion. But if you want to burn something more efficiently some knowledge of the impact on air or oxygen to wood and proper "mixing is important. Is you want to partially burn to form "synthesis gas" (CO and H2) to be used to produce other Hydrocarbons you will need some knowledge of the chemistry, the kinetics and the thermodynamics. If you want to minimize soot formation some knowledge of the mechanism to produce soot is necessary. The amount of kinetics and other fundamental information you need to know about combustion is highly dependent on the purpose of your activity/investigation.
Thermogravimetric analysis (TGA) is one of the techniques that can be used for the evaluation of thermal decomposition behavior of biomass during pyrolysis process. During the analysis, change of the weight of a sample versus time can be measured in heating rates lower than 50 k/min (slow pyrolysis). This technique has limitations such as working under low heating rates and small amounts of samples. Various kinetic models have been proposed by researchers that can be used to obtain kinetic parameters of biomass pyrolysis. The kinetic parameters can later be used to obtain the pyrolysis rate which is an important parameter for the design of the pyrolysis reactor. The calculated pyrolysis rate will be used in the mass balance equation in order to calculate required volume of the reactor which can be either batch or continuous.
In my opinion, kinetics is a kind of method, may be the simplest, which can connect micro scale and macro scale. However, n-order kinetics (one, two, or 1.X) is NOT a wise way because mass action law is valid only when the process is reaction controlled and futthermore in phenomenological area. A lot of work should be done on the connect method, but I don't think TGA is a proper way to get connect method because there are so many heat transfer and mass transfer limitations in the crucible.
Kinetics+Hydrodynamics+Heat transfer model = reaction space (residence time). In fact, this model is very complicated and needs experimental data to prove its validity. Experiments with TGA provide a good understanding what to expect in real practice. Deriving just a kinetic formula substantiate only a publication in a scientific journal. This is my personal opinion.
Kinetict modelling provides better understanding of process mechanism, it is also fundemental for process scaling up.
The final effect of kinetic studies should be the kinetic equation/s. To achieve this, it is necessary to carry out tests for various concentrations of initial substrates, sometimes also with the addition of products, different temperatures, different pressures (reactions in the gas phase), different flow rates (flow systems) etc.
Thermogravimetric studies are performed in non-isothermal conditions. On the basis of the obtained single TG curve and the equivalent DTG, one can estimate the value of various parameters, but actually these are some non-physical meaning numbers. Often, for example, different values of E are obtained in the function of T. They can be averaged and treated at most as a measure of the process's sensitivity to temperature, not activation energy. Sometimes deconvolution of the DTG curve helps, but not always.
In addition, kinetic studies, completed correctly selected kinetic equation/s are just a stage in the problem called scale change. Regards,
Dear Abdul Raheem
The relevance of kinetics can be attributed to the fact that it provides evidence for chemical process mechanisms. Awareness of reaction mechanisms is useful in determining the most efficient way to cause a reaction to occur, in addition to being of inherent scientific interest.
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