亲油性纳米ZSM-5分子筛的制备及其对碳氢燃料的催化性能

Preparation of nano ZSM-5 with hydrophobic surfaces and application to catalytic cracking of hydrocarbon fuels

采用不同链长的有机硅烷作为表面修饰剂，在正庚烷／正丁醇中利用溶剂热合成法制备得到亲油性纳米ZSM-5分子筛．通过有机硅烷与氧化物晶种表面的羟基作用，其长链化学键合到晶种表面，形成保护层，既抑制了氧化物颗粒间的团聚，又控制了纳米ZSM-5的粒径．所制备的纳米ZSM-5平均粒径为20～70nm，且粒径随着有机硅烷碳链长度的降低而逐渐减小．添加一定量的该纳米ZSM-5到碳氢燃料模型化合物正十二烷中，在管式反应器中（550℃，4MPa）考察催化裂解行为，结果表明该亲油性纳米ZSM5分子筛能有效催化正十二烷裂解，其裂解转化率相对于热裂解明显提高，且转化率的提高随着有机硅烷碳链长度的降低而逐渐增大，其中丙基三甲氧基硅烷修饰的ZSM-5使正十二烷的裂解转化率相对于热裂解提高了115％．

Nano ZSM-5 catalysts with hydrophobic surfaces have been prepared by solvent-thermal treatment with an n-heptane/n-butanol mixture as the solvent and different silanes （trimethoxy（propyl）silane, trimethoxy（octyl）silane and hexadecyltrimethoxysilane） as surface modification agents. In order to avoid drastic aggregation, long-chain organic groups are chemically bonded to the surfaces of nano ZSM-5 seeds before the crystallization. The average par- ticle sizes prepared with organosilica are 20 - 70 nm and slightly decrease with the length decrease of the carbon chain. The catalytic cracking behaviors of n-dodeeane, as one model of hydrocarbon fuels, dispersed with nano ZSM- 5 are studied in a tubular reactor at 550℃ and 4 MPa. The results show that the conversions of catalytic cracking are obviously larger than those of thermal cracking, indicating that nano ZSM-5 catalysts have good performance in the catalytic cracking of n-dodeeane. The conversion increases with the decrease of the carbon chain length. The conversion of n-dodecane catalyzed by ZSM-5 prepared with propyltrimethoxysilane is 115~ larger than that of thermal cracking.