The influence of experimental errors during laboratory evaluation of FCC catalysts

The well-known microactivity test (MAT) ASTM D 3907-92, has been used world wide in laboratory scale testing to determine the activity and selectivity of fluid catalytic cracking (FCC) catalysts. To assess catalytic selectivit ies by interpolation, either a kinetic model or functional (empirical) rela tionships between product yields and conversion should be used. Experimenta l errors may significantly affect analysis and erroneous conclusions might arise, justifying application of statistical methods. Although these method s are well established, they are frequently neglected or oversimplified in catalysis. The aim of the present work is to evaluate the influence of typi cal experimental errors from MAT units on interpolated yields, based on pre viously tested empirical functions and data from the literature, and from F CC catalyst samples from PETROBRAS Research Center, with and without a vana dium trap additive. Statistical criteria to identify possible outliers and the confidence intervals for predicted values are discussed. It is shown th at the experimental errors on the independent variable, sometimes disregard ed, drastically decrease the discrimination capacity of the MAT test concer ning iso-conversion and iso-coke evaluations. Concentrating experiments nea r the conversion region of interest and improvement of MAT repeatability co uld mitigate this unavoidable problem. These conclusions can be generalized to selectivity analyses related to the reaction systems other than catalyt ic cracking. (C) 1999 Elsevier Science B.V. All rights reserved.