ZSM-5 additive in fluid catalytic cracking. 2. Effect of hydrogen transfer characteristics of the base cracking catalysts and feedstocks

The effect of hydrogen transfer reactions on ZSM-5 additive in a fluid catalytic cracking system was investigated. Microactivity testing of 4 wt % of ZSM-5 additive on 10 different commercial FCC gas oil feeds showed that the percentage increases of propylene and butylene due to ZSM-5 additive decreases with increasing naphthenes in the feed, due to the high propensity of naphthenes to donate hydrogen. The hydrogen transfer reactions tend to saturate the olefins or olefin precursors which otherwise could be cracked by ZSM-5 into the desired LPG olefins (propylene and butylene). The effect is also confirmed by a model compound study with adamantane. A high content of rare earth on zeolite provides higher acid site density, thus promoting hydrogen transfer. The effectiveness of ZSM-5 is the highest with the catalyst having the lowest acid site density or lowest rare earth level on zeolite.