A four parameter model based on the catalyst aging theory of Wojciechowski(5) is applied to experimental conversion data in gas oil cracking. The data extends over a range of cat/oil ratios from 0.094 to 3.0, and run times from 1.25 to 40 minutes. Within this range of conditions the model is applied to data with and without thermal conversion and excellent correlation between experimental results and calculated values is obtained. The technique for fitting data to the model is described in some detail.

Wojciechowski's four parameter model of catalyst decay is applied to conversion data for gas oil cracking over a diffusion limited catalyst. The parameters thus obtained are compared with those obtained previously for a diffusion free form of the same catalyst, cracking the same feed stock under identical experimental conditions. The comparison shows that the presence of diffusion affects not only the rate of catalytic cracking but also the rate of aging. It is also shown that the introduction of diffusion phenomena has no effect on the mechanism of aging. The presence of diffusion limitations however has the effect of making the feed stock appear more homogeneous in reactivity

A six-parameter multiresponse model based on the catalyst aging theory of Wojciechowski (1968) is applied to experimental selectivity data in gas oil cracking. Within the range of conditions studied, the model gave an adequate fit to the data. It was found that the selectivity curves at various cat/oil ratios were contained within optimum and minimum performance envelopes but that the relationships between these envelopes and the selectivity curves were not quite as simple as had previously been reported for a theoretical example (Campbell and Wojciechowski, 1969). The optimum time-on-stream for each of the cat/oil ratios was about one minute. Maximum gasoline production was 59 weight yo at 81 weight 7 ' total cumulative conversion, resulting in a gasoline efficiency of 72.8y0.

Gasoline selectivity in the catalytic cracking of four neutral distillates, varying only in wax content, has been studied over a range of temperatures. It has been found that the cracking rate constants leading to gasoline and to undesirable products, as well as the gasoline recracking rate constant, increase linearly with the mole fraction of wax in the feed. At the same time the activation energies for the primary rate constants decrease with increasing wax content of the feed, while the activation energy for gasoline recracking is not affected by feed composition. We also find that the various components of the feed crack quite independently of one another and do not interact in any way. There appears to be no synergistic interactions between the wax‐free fraction and the wax in the feed. In spite of the large difference between reaction rate constants reported here and those previously reported for the cracking of a mid‐continent gas oil by Pachovsky and Wojciechowski16, the Optimum Performance Envelopes for all the chargestocks we have studied are very similar. Our results indicate that the major differences between gas oils we have studied lie in their “reactivity”; in other words, in their relative rates of conversion at a given set of conditions.

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