ULTRA-SELECTIVE FCC PROCESS WITH DOWNFLOW REACTOR AND OPTIMIZED CATALYST SYSTEM

摘要

Many recent developments in the FCC area have focused on reducing the contact time between catalyst and hydrocarbon vapor to improve product selectivity: lower delta coke on catalyst, and higher selectivity to gasoline and light olefins. Nevertheless, very special conditions should be used to benefit from such short reaction times, as clearly indicated in pilot tests carried out at PETROBRAS. The downflow reactor provides significant selectivity advantages, mainly in terms of coke and olefins, due to its much more uniform gas-solids flow pattern. However, in downflow reactors, the catalyst residence time and catalyst holdup is lower, considering the same hydrocarbon residence time used in a riser. Thus, for obtaining the adequate conversion levels, higher catalyst to oil ratio, higher reaction temperature or more active catalyst would be necessary. Fortunately, the continuing development of new catalyst technologies has made possible to work with downflow systems without any harm on conversion levels, using regular FCC operating conditions. Experimental studies carried out at a pilot downflow unit, using a pilot riser unit as reference, showed advantages in conversion, LPG and propylene. Following these studies, PETROBRAS will revamp one of its FCC units into a downflow catalytic cracker.