Study on the preliminary cracking of heavy vacuum gas oil: Effect of acid type and contacting order of Lewis and Brönsted sites of matrices on the yield of LPG olefins

A series of alumina with similar textural properties but different acidities were prepared and used as the matrix components of the FCC catalysts. The effect of acid type of matrices and contacting order of acid sites of different types on the yield of LPG olefins in catalytic cracking of heavy vacuum gas oil (HVGO) was investigated. The results showed that the matrix is more conductive to the formation of LPG olefins from the aspect of reaction route, in comparison with the REUSY molecular sieves. When there are Brönsted acidity on the matrix surface and/or HVGO molecules first contact with Lewis acid sites and then react with Brönsted acid sites during the matrix-precracking process, cracking reactions are enhanced while hydrogen transfer reactions are restricted, which facilitate to increase the yield of LPG olefins.