McCarty Reaction Kinetics

The McCarty and Green method is of economical interest because only one test run is required for the calculation of reaction kinetics. 

Fig. 3-65 Reaction Kinetics according to McCarty and Green [3-24] Pyrolysis of CaCjO HjO Heating Rate ]3 10 K/min...

MCCARTY Energetics and Kinetics of Treatment Various Half-Reactions... 

Following earlier work in which the intermediate in the formation of methane from carbon monoxide and hydrogen was found to be carbon, McCarty and Wise carried out a thorough study of the system. Four types of carbon were found to be formed from carbon monoxide on nickel at 550 50K. Chemisorbed carbon atoms reacted readily with hydrogen as did the initial layers of nickel carbide. Further deposits of the carbide, amorphous carbon, and crystalline elemental carbon were much less reactive and the kinetics of the reaction should be described by the established rate laws. Conversion of the more active to the less active forms of carbon occurred above approximately 600 K. 

Further development of kinetic models for the OCM process followed the path of addition of a limited number of heterogeneous steps (first of all— initiation or generation of primary methyl radicals) to homogeneous schemes of methane oxidation (Aparicio et al, 1991 Hatano et al, 1990 McCarty et al, 1990 Shi et al, 1992 Vedeneev et al, 1995 Zanthoff and Baerns, 1990). There was certain logic in such an approach since the most efficient OCM catalysts are almost exclusively oxides with no transition metal ions (some Mn-contain-ing oxide systems are the only exception), any reactions in adsorbed layers at such temperatures can be neglected. In the framework of such models some substantial features of the process could be described. For instance, they predicted the limit in the C2-hydrocarbon yield close to that reliably observed experimentally over the most efficient catalysts (20-25%). 

The application of thermoanalytical methods to the investigation of the kinetics of pyrolysis and oxidation processes of heavy petroleum components representing multi-component systems proved to be successful. Whereas the ASTM E 698-79 and the Flynn and Wall methods can be applied relatively uncritically, the interpretation of the data from the McCarty and Green method requires a solid knowledge of the thermal and oxidative behavior of the samples. The attempt to use the evaluation according to Borchardt and Daniels proved not to be successful for pyrolysis nor for oxidation reactions. Most of the... 

McCarty [125] used an annular reactor to evaluate kinetics of methane combustion over PdO-supported catalysts. The design of the apparatus had a small gap between cylinders (0.1-0.3 mm) and a thin coating (10 pm). Using high flow rates and dilute methane and oxygen in helium, the author claims to have measured the intrinsic rate of methane oxidation up to 900°C, without contributions from gas-phase reactions. Groppi et al. 

---