Catalyst Decay quantifying

Wojdechowski, B.W. (1998) The reaction mechanism of catalytic cracking quantifying activity, selectivity, and catalyst decay. Catal. Rev. — Sci. Eng., 40, 209. 

Using this picture of the chemical events involved in catalyst decay, we can quantify the consequences of such behaviour without any prior knowledge of the activity of each of the many species which may be formed in this way. To do this, we use the concept and the mathematics of Markov chains, a mathematical construct which allows for the wide variety of processes described above to be systematized and considered in quantitative terms. 

The kinetics of feed conversion, minor product formation, and catalyst decay in catalytic cracking are well-described in a unified hypothesis by quantifying the fates of the carbenium ions which one expects to find in a given catalytic cracking reaction. 

It is also assumed for now that there is no significant catalyst decay or activation during an experiment. Such activity changes can be quantified in some cases using temperature scanning methods, and these will be considered later. 

Figure 11.19 shows the process flow sheet for a pilot-scale fluidized bed gasifier, capable of processing some 20 kg/h of biomass feed, coupled with a thermal cracker and reformer reactor. The reformer is loaded with fluidizable nickel-based reforming catalyst and fitted with gas analysis ports at its inlet and outlet. The system has been used to evaluate catalyst activity and the decay of hydrocarbon conversion with time from a slip stream sample of the raw fuel gas. In this way, it is possible to quantify the frequently reported phenomenon of commercial catalyst deactivation, sometimes quite rapid, from high activity of fresh samples to lower residual activity brought about by various factors, including the presence of poisons (sulphur, chlorine) and coke formation. 

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