Cr改性USY分子筛提高裂化催化剂的异构化性能

在催化裂化过程中，烷烃分子在酸性催化剂表面进行一系列的反应，其中氢转移反应能导致汽油中的烯烃质量分数降低，而异构化、环化、芳构化反应则改善裂化产品的分布，对提高裂化汽油的辛烷值有明显的效果。为了解决我国裂化汽油中烯烃质量分数过高的问题，目前大多数催化裂化装置都采用了降烯烃裂化催化剂，以氢转移反应活性高的REUSY分子筛作为裂化催化剂的活性组分。但由于REUSY分子筛的异构化活性较低，因此裂化汽油的辛烷值有所下降，需要对裂化汽油进行加氢异构化处理。若直接对裂化催化剂进行改性，提高其异构化反应活性，

Promoting isomerization activity of USY cracking catalyst by chromium modification

In order to reducing olefin fraction in FCC gasoline, USY zeolite, the active component of FCC catalyst, was modified by impregnating or ion-exchanging chromium. Acidity and cracking activity of modified USY zeolite were studied by IR and MAT. It was found that both amount and strength of Bronsted acid site on the surface of modified USY zeolite were increased obviously, but the Lewis acid site was almost unchanged. The hydrogen-transfer activity of modified USY zeolite was independent of the ways of loading chromium, but the isomerization activity of USY zoilite was dependent of the loading methods. The impregnated Cr-USY was better than ion-exchanged Cr-USY. The activities for cracking, hydrogen-transfer and isomerization reaction of modified USY zeolite were increased first, and then decreased with increasing of chromium amount. The cracking catalyst, USY zeolite with 0.01% chromium as the active component, showed higher activities for cracking, hydrogen-transfer and isomerization reaction. The olefin content in cracking gasoline was decreased evidently, and the isomeric alkane, cycloalkane and aromatic hydrocarbon were increased. The extent of olefin decline was high to 28 %, but the contents of isomeric alkane, cycloalkane and aromatic hydrocarbon were enhanced in evidence, they were 6.8 %, 20 % and 27.6 % separately comparing to the USY zeolite cracking catalyst. The decreasing of olefin and increasing of cycloalkane and aromatic hydrocarbon improved the octane number of cracking gasoline. It was indicate that the chromium modified USY zeolite was favorable to the olefin-reduce cracking catalysts.