Modelling of selectivity data obtained from microactivity testing of FCC catalysts

The well-known microactivity test (MAT) ASTM D 3907-92 can be used to determine the activity and selectivities of fluid catalytic cracking catalysts (FCC). The assessment of catalytic selectivity is of major importance to the development of FCC catalysts because it determines the selectivity of desired products and unwanted by-products. A procedure has now been developed to evaluate the selectivity data obtained by cracking of vacuum gas oil on FCC catalysts in a microactivity test unit. Lump models and optimum performance envelope curves, which are published in the literature, present the interrelation of conversion and yields. Following these considerations, functional relationships containing only two parameters to be estimated and known boundary conditions were determined empirically, The parameters are estimated by fitting these functions to the experimental data by non-linear least-squares methods. Subsequently, these predicted functions can be used for interpolation purposes. It is shown that the reliability of the estimated parameters and predicted values are considerably improved compared with those obtained by other methods, e.g., curve fitting and data interpolation by flexible ruler or use of second order polynomials. The development of this new approach and the automation of this method for routinely-performed MAT data processing has been realised with the software RS/1. FCC catalysts have been evaluated with this new procedure to demonstrate its applicability on routinely-performed MAT selectivity studies.