Establishment and Kinetic Analysis of an in-Situ Crystallized Catalyst Based FCC Lump Kinetic Model

Nowadays, FCC units face increasing pressure to convert more inferior and heavy oil into clean fuels and light olefins as worsening qualities of feedstock and ever stricter environmental regulations. Undoubtedly, catalyst is always one of the key factors for FCC process and different catalysts could lead to significant differences in product distribution. Besides, compared with technical reform and plant revamp, replacement of the FCC catalyst is the most economical and efficient way for FCC units to obtain a better product distribution. According to the preparation method, FCC catalysts can be classified as semi-synthesized (gel method) and in-situ crystallized FCC catalyst. As reported in some literatures, in-situ crystallized FCC catalyst exhibited attractive prospect for inferior and heavy oil processing, and was featured with better dispersion of zeolites, smaller crystal size of zeolite, better thermal and hydrothermal stability compared with semi-synthesized FCC catalyst.

Currently, BASF Catalysts LLC (former Engelhard Corp.) and Catalyst Plant of China National Petroleum Corporation (CNPC) Lanzhou Petrochemical Corporation are the main two companies providing in-situ crystalized FCC catalyst worldwide, and the research and development of in-situ crystalized FCC catalysts have made a lot of progresses in near half a century. However, most of the studies of catalyst design and corresponding operation optimization were mainly based on personal experience and laborious experiments.

Kinetic study is a powerful tool for a better understanding of the catalyst. As for the complicated FCC reaction system, a method known as lump kinetic modelling is needed. Actually, several lump kinetic models were reported for catalytic cracking of heavy oil. However, those models were generally based on semi-synthesized FCC catalysts and cannot reveal the kinetic characteristics of the in-situ crystallized FCC catalysts. Moreover, lump kinetic modelling can easily provide useful insights into operation optimization without laborious experiments. Hence, it is necessary to establish a lump kinetic model of the in-situ crystallized FCC catalyst.

In this work, the kinetic characteristics of an in-situ crystallized FCC catalyst were reported for the first time. A six-lump kinetic model containing 24 kinetic parameters, one parameter for basic nitrogen poisoning, another parameter for aromatics adsorption and other two parameters for catalyst deactivation was established. Kinetic parameters were estimated based on experimental data at 460, 480, 500 and 520 °C by fourth order Runge-Kutta algorithm and the least square method. Frequency factors and apparent activation energies were then calculated according to Arrhenius equation. The predicted data of product distribution showed good agreement with experimental data, and the relative errors were mainly within 10 %. Model analysis indicated that a relative low temperature was more suitable for the production of light oil.