磷改性杂原子B-ZSM-5分子筛催化剂结构及其在液化气芳构化的应用

Effects of phosphorus-modification on the structure and catalytic activity of boron substituted ZSM-5 molecular sieves for aromatization of LPG

水热合成了杂原子硼ZSM-5分子筛,利用浸渍法制备了系列不同磷含量的HB-ZSM-5催化剂,并用于液化气的芳构化反应。考察了不同磷含量对芳构化反应性能的影响,并与吡啶吸附红外光谱(FT-IR)和固体核磁(NMR)相关联,研究了磷改性处理对催化剂表面酸性的影响。结果表明,磷改性HB-ZSM-5的芳构化活性得到改善。与未经磷改性处理的催化剂相比,550℃热处理的3.3PHB-ZSM-5催化剂在一定反应条件下芳构化反应4 h,烯烃转化率为90.5%,液收中芳烃质量分数为23.5%。随着磷含量的增大,B酸中心数升高,L酸中心数减少。烯烃转化率和芳烃收率升高,磷含量3.3%的HB-ZSM-5催化剂达到最大值,表明此时B酸中心和L酸中心比例协调性最佳。

Borosilicate molecular sieves with MFI structure were synthesized by hydrothermal method. HB-ZSM-5 molecular sieves modified with orthophosphoric acid were prepared by impregnation method and were used in aromatization of LPG. The as-prepared samples were characterized by X-ray diffraction, FT-IR, nitrogen adsorption, n B and 31p MAS NMR technique. The effects of the phosphorus-modification on surface acidity of HB-ZSM-5 were investigated. The results showed that the aromatization activity of phosphorus modified HB-ZSM-5 molecular sieves was improved; alkenes conversion of 90. 5% and aromatics yield of 23.5% were attained over 3.3PHB-ZSM-5 molecular sieves by heat treatment at 550 ℃ and aromatization for 4 h; with the increase of P content in HB-ZSM-5 molecular sieves, the amount of Brfinsted acid sites was enhanced and the amount of Lewis acid sites was decreased,and alkenes conversion and aromat- ics yield were increased;3.3PHB-ZSM-5 molecular sieves had maximum alkenes conversion and aromat- ics yield, which indicated that the best coordination between Bronsted and Lewis sites was attainted.