HIERARCHICAL ZEOLITES: INCREASE IN MESOSURFACE VIA “BOTTOM-UP” OR “TOP- DOWN” METHODS AND ITS INFLUENCE IN CATALYTIC CRACKING

摘要

The Fluid Catalytic Cracking (FCC) is still the most important refinery operation, converting heavy feedstock into more valuable products such as gasoline, diesel and LPG. The FCC catalyst is a key point in the optimization of FCC units. Although the FCC capacity has been increasing, the quality of the processed feed has been deteriorating worldwide. Indeed, an increase in average density, RCR and metals content (Ni, V and Fe) has been observed. In order to convert refractory feedstock into valuable products, it is important to enhance the conversion of heavy molecules present in the feed. Hence, one must reduce the diffusional constraints present in both the active matrix and zeolite. Regarding Y zeolites, the main components of FCC catalysts, the adopted strategy to cope with cracking of heavier molecules was the development of methods to increase mesosurface area, via the following methods1: a) The synthesis of zeolites with larger micropores; b) reduction of the crystal size; c) introduction of additional pores of larger sizes (mesopores). Such methods may be divided into two categories: “Top-down” or post-synthetic modification and “bottom-up” or primary syntheses.