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Turbulent Flames and Fire Plumes
Published in Bart Merci, Tarek Beji, Fluid Mechanics Aspects of Fire and Smoke Dynamics in Enclosures, 2023
However, it was explained in Section 2.2.3 that a sufficiently high temperature is required for combustion reactions to take place at a notable rate. This relates to the ‘activation energy’. Indeed, as explained in Section 3.1.1, a ‘threshold’ temperature can be estimated below which the reactions are ‘quenched’. The higher the activation energy, the higher the temperature needs to be for reactions to take place at a notable rate. This is addressed in more detail in Sections 3.1.1 and 3.1.2.
Introduction to Heterogeneous Catalysis in Organic Transformation
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Gyandshwar Kumar Rao, Varun Rawat, Ved Prakash Verma, Kaur Navjeet
The concept of the term “Catalysis” was first described by Berzelius in 1835 [1] and later defined scientifically by Ostwald in 1894 [2]. However, catalysts have been used for thousands of years and the oldest example that we still encounter today is the fermentation process which the Egyptians first discovered to produce wine [3]. Catalysis has been the backbone of industrial applications and is used extensively in manufacturing agro- and petrochemicals, cosmetics, pharmaceuticals and medicines, polymers, aliments, and many more [4]. By definition, a catalyst is a substance that can increase a chemical reaction’s speed without undergoing any change itself. Figure 1.1 gives a very simplistic view of the energetics involved in a catalyzed reaction. A catalyst can change the reaction pathways that lower its activation energy and increase the rate of reaction. However, a catalyst does not alter the equilibrium of a reaction, which means that the product formation is achieved at a faster rate, whereas the yield of the reaction remains unaffected. A catalyst undergoes a reversible chemical change, and it regenerates its previous form at the end of a chemical cycle.
Metabolism
Published in Volodymyr Ivanov, Environmental Microbiology for Engineers, 2020
The activation energy is the minimum amount of energy required to initiate a chemical reaction. An enzyme significantly decreases the energy of activation of a reaction due by stereochemical arrangement of a substrate inside the 3D structure of a protein, which is favorable for the initiation of the reaction. A decrease in activation energy increases the rate of the reaction (Figure 2.9). Typically, enzyme-catalyzed biochemical reactions are a thousand or even a million times faster than the same chemical reaction without an enzyme.
Waste bone char-derived adsorbents: characteristics, adsorption mechanism and model approach
Published in Environmental Technology Reviews, 2023
Abarasi Hart, Duduna William Porbeni, Selina Omonmhenle, Ebikapaye Peretomode
h0 is the initial adsorption rate. If the second-order kinetics is applicable, then the plot of t/qt against t in equation (10) should give a linear relationship from which the constants qe and h0 can be determined. It also suggests several mechanisms are involved in the adsorption process. However, in these kinetic models, the adsorbed amount qe changes with temperature (i.e. a thermodynamic equilibrium quantity), so the temperature dependence of the rate constant needs to be accounted for in the models. Hence, the activation energy can also be estimated with the Arrhenius equation and rate constants for various temperatures. Using the Arrhenius equation (11), the activation energy (Ea) and pre-exponential factor (A) of the adsorption process can be determined numerically. Other adsorption kinetics models used to study BC adsorption kinetic include Ritch-second-order, Elovich equation, and intra-particle diffusion model [63], as shown in Table 2. Where; Kads denotes adsorption rate constant, T is temperature (K), and R constant. The plot of ln Kads versus 1/T is linear from which Ea and A would be determined.
A comprehensive thermo-kinetics devolatilization analysis of waste motor oil: Thermal degradation kinetics, kinetic model, thermodynamic analysis, and ANN
Published in International Journal of Green Energy, 2023
Asmita Mishra, Mayuri Sonowal, Venkata Yasaswy Turlapati, Payal Maiti, B.C. Meikap
The activation energy for the pyrolysis of WMO using the Coats-Redfern method ranges invariably between 25.2 and 116.969 kJ mol−1. These values were obtained using the diffusion control (Janders), contracting sphere, first-order, third-order, and Avrami-Erofeev models for all heating rates. The pre-exponential factor and activation energy are both known to be related to material structure and reactivity, respectively. High-activation-energy reactions necessitate higher temperatures or longer reaction durations. Therefore, it is critical to determine which model is most appropriate for modeling WMO pyrolysis. As seen in Figure 4(a), almost all models, except for the “Third order” model, exhibit a linear trend with correlation coefficients ranging from 0.988 to 0.9967. Although the |r| values reported by different models for different samples varied, they were all relatively high. Suppose the diffusion control model is considered the reaction model. These results demonstrated that the Coats-Redfern method’s accuracy is unsatisfactory and cannot be utilized to evaluate the reaction kinetics of WMO. As a result, judging which model is best based on the value of |r| is nearly impossible.
Effect of mineral phases on the leaching efficiency of Ti slag
Published in Canadian Metallurgical Quarterly, 2023
Haibo Wang, Ke Sun, Bin Wang, Ruifang Lu, Xiaoping Wu
The activation energy of the leaching reaction in this work was determined to be 69.87 kJ/mol. For comparison, the activations energy values reported previously are listed in Table 5. Activation energy is the minimum amount of energy needed to start a chemical reaction. It can be seen from Table 5, under the moderate temperature and moderate acid concentration conditions, the leaching reactions of titanium slag or ilmenite are restricted by chemical reaction and other possible factors such as phase boundaries. The activation energy values are high, ranging from 64.4 kJ/mol to 90 kJ/mol for ilmenite and Ti-bearing slag. However, under the conditions of high temperature and high acid concentration, HTBBF slag becomes highly reactive, and the activation energies of these leaching reactions are reduced very significantly.