Activation energy gasification reactions

Gasification by hydrogen atoms proceeds with an activation energy of about 40kJmol". The activation energy for reaction with nitrogen atoms is higher, at about 75 kJ mol . ... 

The kinetic parameters for the n order kinetic model have been obtained using these definitions of reactivity for the pure steam gasification experiments of birch. All the activation energies lie between 228-238 kJ/mol and the reaction orders between 0.54 and 0.58, apart from definition 3. The frequency factors are somewhat more scattered, lying between 5-10 and 3-10 . Regarding the uncertainty of the calculation, definitions 2, 5 and 4 seem to give more precise results and it is interesting to notice that the error of the reaction order calculation does not depend on how a representative reactivity value is defined. 

Gasification of coke by hydrogen, then, can be seen to be a complex process in which a surface reaction is important at low temperatures (< 550 °C). In the range 550-600 °C, the surface reaction is also important but the rates seem to be affected by pore diffusion. Above 700 °C the apparent activation energy is negative and this seems to result from the approach of the system to equilibrium. 

For the experimental conditions of temperature, water vapour partial pressure and gas flow rate examined the kinetics of gasification of the ESC deposit were consistent with previous observations for the carbon-water vapour reaction (7,8). The reaction was chemically controlled and the oxidation rate was linearly dependent upon water vapour partial pressure. The measured activation energy (57 Real mole-1) was in the middle of the previously reported values (13.5 (JO-83 (9) Real mole-1) for this reaction. 

Gasification Kinetics of Coke Deposited on Silica-Alumina. Within the temperature range 1400 to 1600°F and in the presence of excess steam, the gasification reaction of coke deposited on the silica-alumina cracking catalyst closely followed first-order kinetics with respect to unreacted carbon (Figure 1). First-order rate constants were calculated from the slopes of these plots (Table III), and yielded an activation energy of 55.5 Kcal/mole. 

The activation energies for coke gasification on the three substrates shown in Figure 4 were 33 Kcal/mole for the three alumina-based materials and 54 Kcal/mole, for the silica-alumina catalysts. The increased activity and lower activation energy for the coke deposited on the aluminas (compared to that on the silica-aluminas) cannot be due to a direct catalytic effect of alumina on the gasification reaction, but rather to an indirect effect of the alumina that controls the nature and structure (surface area and structural disorder) of the coke during its deposition. 

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