A Study Of Low Coke Yield Catalyst For Resid Fluid Catalytic Cracking

Fluid catalytic cracking (FCC) process is a central technology in morden petroleum refineries. While originally designed for cracking the overhead stream from vacuum distillation units (VGO), most FCC units currently operate with some higher boiling vacuum distillation bottoms (resid) in the feedstock. Designing catalysts to tolerate heavier feedstock, while still maintaining high conversion and low coke yield, is a key issue of the FCC catalyst design.To meet the requirements for improving activity and enhancing coke resistance property of catalyst for resid fluid catalytic cracking (RFCC), series of ultrastable Y zeolites with high Si/Al ratio and micro-sphere catalysts based on the resulted zeolites have been prepared. The catalytic profermonces of the dealuminated Y zeolites and the catalysts have been investigated in this paper.It is found that the amount of acid sites of dealuminated Y zeolites could be effectively adjusted by dealumination using chemical reactant followed by hydrothermal treatment. Therefore, dealuminated Y zeolite with suitable amount of acid sites and definite acidity could be expected. After being modified by lanthanum incorporation and aged, the dealuminated Y zeolites were characterized, and their catalytic cracking performance were evaluated with microactivity test (MAT). It is shows that the samples prepared by using oxalic acid as dealumination reactant, combined with hydrothermal treatment (LaOSY) have large mesopore volume. Although the LaOSY sample exhibits better liquid yield selectivity in resid MAT at high cat./oil ratio, its cracking activity for diesel oil MAT is relatively low. However, the samples prepared by using (NH4)2SiF6 as dealumination reactant, combined with hydrothermal treatment (LaFSY) have homogeneous framework aluminum distribution, and therefore a LaFSY zeolite with suitable strong acid sites and less weak acid sites was obtained. After being aged at 800℃ in 100% steam for 17 h, the LaFSY zeolite exhibits higher cracking activity and lower coke yield compared with the general industrial REHY.Micro-sphere catalysts composed of the LaFSY zeolite and matrix have been preparedand several parameters such as the content of zeolite, the amount of lanthanum incorporation to zeolite and the type of matrix were also invesgated. As a result, a catalyst sample compoed of 45% of LaFSY that contains 4% of lanthanum oxide, using alumina sol and gaolin clay as matrix was obtained. After being aged at 800℃ in 100% steam for 17 h, the catalyst shows higher activity for diesel oil MAT. More importantly, it exhibits higher light yield and lower coke yield in the RFCC reaction while using Daqing resid as feedstock, compared with the general industrial catalyst LBO-16. Therefore the catalyst could be considered as a better catalyst for resid fluid catalytic cracking.