Kinetics according to McCarty and Green

The method of McCarty and Green is most useful since only one TGA experiment is required, but selection of the correct hmits for the integration raises problems. If the limits are set to the two horizontal branches of the TGA curve, for example to 250 °C and 520 °C, then the values of the kinetic parameters of bitumen B80 will be far too small as shown in Fig. 4-206 with E = 120.18 kJ/Mol and log A = 8.160 min .  

When applying low heating rates the kinetic parameters do not show any significant dependence on the heating rates (Table 4-206, bitumen B80). Table 4-207 shows the kinetic parameters of VR Kuwait and its components. The values for evaporation of the asphaltenes are already in the range of a pyrolysis reaction. The curve of pyrolysis of the petroleum resins shows two reaction regions with different slopes (Fig. 4-208). The first onset appears at 432 °C. The offset point of this branch of the curve is at the same time the 

Heating rate (K/min) Temperature limits ( O E (kJ/Mol) log A (min ) Weight loss at the upper temperature hmit (%) 

Experiments with Simultaneous Thermal Analyzer. Heating Rate j8= 10 K/min 

The oxidation reaction is a more complicated process than pyrolysis. In DTA or DSC the oxidation of pure chemicals always reveals three or more maxima at different temperatures in the plot of heat flow versus temperature. The TGA curves display more than one point of inflexion and the DTG and DSC (DTA) curves more than one peak maximum (Fig. 4-209 and 4-210). 

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

Table 4-207 Pyrolysis kinetics according to McCarty and Green.

Fig. 3-66 Kinetic of Vaporization of /i-Alkanes according to McCarty and Green Atmosphere Argon, 30 + 20 cmVmin, 1 bar Heating Rate p 10 K/min X Integration Limits On.sct Point to Offset Point o Integration Limits 100 % Weight to Onset Point...

Table 4-206 Pyrolysis kinetics of bitumen B80 according to McCarty and Green. Experiments with Simultaneous Thermal Analyzer...

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... 

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