In the kinetic study of char in the spent catalyst (C : 38 wt.\%, S: 4.8 wt.\%) and $O_2$, the effects of regeneration or combustion temperature (550 $^\circ$C - 750 $^\circ$C) and partial pressure of $O_2$ (0.09 atm - 0.21 atm) on combustion reaction rate have been determined in a thermobalance reactor. Among the reported models (shrinking core, volumetric and modified volume reaction models), the modified volume reaction model is the best to predict the present conversion data. The kinetics parameters (activation energy, pre-exponential factor and reaction order) are determined on the basis of the modified volume reaction model. From the Arrhenius plot, the activation energy and the pre-exponential factor are found to be 19.810 kJ/mol and 15.738 l/min respectively. The reaction order is found to be 1.41 with respect to $O_2$ partial pressure in the range of 0.09 atm - 0.21 atm at 650 $^\circ$C. The combustion reaction rate of char in the spent catalyst with $O_2$ can be expressed as:
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In regeneration of the spent catalyst, the effect of reaction time (0 min - 50 min) as a function of conversion (0 - 1) on surface area, pore volume and average pore diameter of the catalyst have been determined in a thermobalance reactor. The spent catalyst is regenerated in terms of physical properties by removal of coke by combustion.
The regeneration characteristics of the spent catalyst have determined in an ICFB (Internally Circulating Fluidized Bed - 0.3 m I.D × 3 m high) with a draft tube (0.1m I.D × 0.9 m high). In the ICFB, the axial temperature profile is uniform at the annulus gas velocity (Ua) above 0.8 Umf (minimum fluidization velocity) or the excess air for combustion above 53\%. The removal rates of carbon and sulfur in the spent catalyst increase with increasing combustion temperature. However, the removal rates of carbon and sulfur in the spent catalyst increase marginally at temperature above 550 ℃. Also, the removal rates of carbon and sulfur in the spent catalyst are found to be insignificant with increasing gas velocity in the draft tube (Ud). The removal rate of carbon increases with increasing Ua up to 1.2Umf and levels-off thereafter. The removal rate of sulfur in the spent catalyst increases with an increase in Ua due to the increase of excess air for combustion. As excess air increases, the removal rate of sulfur in the spent catalyst increases due to prevention of $SO_3$ or $SO_4$ formation on alumina support and the removal rate of carbon increases insignificantly above the excess air of 96\%. The removal percentage of carbon is found to be 99.4\% and the weight percentage of carbon for the regenerated catalyst is 0.2\%. Surface area after regeneration of the spent catalyst is found to be 114\%. It can be claimed that the present ICFB process is better than the other processes for regeneration of the spent catalyst based on the carbon removal rate and surface area recovery of the catalyst.
