草酸脱铝改性USY的表征及加氢裂化性能

采用草酸脱铝对USY分子筛进行了改性,考察了草酸加入量对USY相对结晶度(CRX)、硅铝比(nS iO2/nA l2O3)、比表面积、孔结构及加氢裂化性能的影响,并采用程序升温脱附和原位红外光谱技术对改性USY型分子筛的酸性进行了表征。结果表明,随草酸加入量的增加,在脱除USY中非骨架铝的同时,骨架铝被脱除的量也逐渐增多,致使USY的相对结晶度先提高而后降低、硅铝比提高、酸强度和酸量降低。正癸烷的加氢裂化结果表明,当草酸的加入质量比为0.2时,正癸烷的转化率和一次裂化产物的选择性分别为68.5%和80.1%。草酸改性USY具有高催化活性是因为该分子筛具有空旷的介孔结构和较多的可接近的酸性位;一次裂化产物选择性高是因为空旷的介孔结构使裂化产物快速离开酸性位而避免了二次裂化。

Hydrocracking performance of USY modified by dealumination with oxalic acid

USY zeolite was modified by dealuminization with oxalic acid. The effects of oxalic acid amount used for the modification on the relative crystallinity, SiO₂/Al₂O₃ molar ratio, specific surface area, pore structure, acidity, and performance in decane hydrocracking of the resultant USY were investigated. The results showed that accompanying with the leaching of non-framework aluminum, some framework aluminum is also leached out from the modified USY zeolite; therefore, with the increase of the oxalic acid amount used, the SiO₂/Al₂O₃ ratio of the modified USY is increased, the acidic strength and acidic amount are decreased, while a maximal relative crystallinity is obtained at a moderate amount of oxalic acid. For the hydrocracking of decane over the USY zeolite modified by oxalic acid of 0.2 (mass ratio), the conversion of decane and the selectivity to primary cracking products are 68.5% and 80.1%, respectively. The high hydrocracking activity of the modified USY can be attributed to its mesoporous structure and abundant accessible acidic centers; moreover, the large pores is also favorable for the diffusion of primary cracking products to avoid secondary cracking, which may also enhance the selectivity of primary cracking products.