Study On Synthesis And Catalytic Performance Of Core - Shell USY @ AlSBA - 15 Composites

Crude oil is an important source of energy; and catalytic cracking is the core technology in the oil refining industry. USY zeolite with large pore of1.1nm is usually used as the active component of cracking catalyst in industry. With the exhaustion of oil resources, the increase of the proportion of heavy oil and the further decline of oil quality, cracking catalyst must have larger pore size. Dealumination is usually used, but does not meet the requirements, because of lacking secondary pores, low crystallinity and low silica/alumina ratio. Mesoporous A1SBA-15materials have large pores of4-10nm; however, catalytic cracking performance is very weak. Here in this paper, core-shell structure of USY@AlSBA-15composites with the core of USY zeolite and the shell of mesoporous A1SBA-15material are synthesized. The cracking reactions of large molecules need the weak acid sites while small molecules require the strong acid sites. This core-shell structure material has multistage channels and acid sites, where weak acid sites on mesoporous AlSBA-15can pre-crack large molecules. Thus the intermediate molecules cracked by the shell can enter the internal pores of USY zeolite, which has strong acidic sites, to crack further to improve the cracking reaction performance. With the existence of multistage channels, cracking products easily spread out from the mesoporous channels for avoiding excessive cracking. Therefore, the reaction selectivity can be improved well.Firstly, because of the synthesis of SBA-15in the strong acid condition, the acid-resistant range of USY zeolite must be evaluated for further in-situ assembly. Then the best way of synthesis of SBA-15is searched on base of above research. Experimental results show that the Br(?)nsted and Lewis acid sites of USY zeolite in HC1solution would decline at both room temperature and hydrothermal conditions. The decline level varies with hydrochloric acid concentration, processing time and temperature. Given a goal of keeping90%of acid amount, the processing time should below4h in0.4M HCl solution at room temperature, while at hydrothermal conditions for24h the pH be higher than2.5.Secondly, the possibility of lower acidity and shorter time synthesis of SBA-15are explored according to the results of the USY zeolite acid resistance research. The approach of pre-hydrolysis of silica resources is used to shorten hydrolysis time. Two separate stages of synthesis of SBA-15are processed in different acid system to adapt the acid resistance of USY zeolite. Optimum synthesis conditions of SBA-15are explored by adjusting the hydrolysis acidity, hydrolysis time, and hydrothermal acidity, which are the synthesis foundation of core-shell type composites.Finally, the core-shell type of USY@AlSBA-15is prepared and hexadecane catalytic cracking reactions are tested. The problem of separation of microporous and mesoporous materials is perfectly solved by creative adjusting reaction temperature, template agent and material concentration. The mesoporous shell thickness could be well controlled from30nm to80nm by adjusting the reactant ratios. Hexadecane catalytic cracking reactions show that the core-shell catalyst has higher liquid yield than the pure USY zeolite or the mechanic mixture of USY and AlSBA-15.