预裂化理论研究:基质表面酸性位类型及不同类型酸性位接触顺序对裂化过程小分子烯烃收率的影响

在区分氢负离子转移反应与氢转移反应、非选择性氢转移反应与总的氢转移反应的情况下,通过合成物性相近但酸性不同的氧化铝,用以作为裂化催化剂基质材料,在固定床反应器上考察了催化裂化过程,基质酸性位类型及基质表面Lewis及Brönsted酸性位接触顺序对小分子烯烃(丙烯、丁烯)收率的影响。结果表明,催化裂化生成小分子烯烃过程中,分子筛与基质所呈现出的反应特点存在较大的区别,前者活性虽高,但总的氢转移反应活性过强。基质材料裂化活性虽低但其表面以氢负离子转移反应为主,反应路径角度更有利于小分子烯烃收率的提高。另外,基质表面存在Brönsted酸性位,或原料油首先与基质表面Lewis酸性位相接触再与Brönsted酸性位反应的预裂化过程,会在促进裂化反应发生的同时抑制总的氢转移反应,更有利于小分子烯烃收率的提高。

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.